[oldalum]

I looked up some facts to clarify the return policy.
 
To leave, you need to apply for an official Leave of Absence. If you leave without a LOA, or if you have a LOA but do not return after you have used up the maximum total of 8 quarters of LOA that are allowed, you will formally become a “Discontinued” student and the University is not obliged to reinstate you (you have to apply for reinstatement, and the bases for that decision are not given). A LOA requires approval by “your undergraduate Advising Director” and by the Dean of Students Office. (I do not know how restrictive those approvals are, but I would guess they have been mostly if not completely permissive). A LOA can be for up to one year, but then you can apply for an additional year (again I do not know how restrictive they are on granting these).
 
While on a LOA, you can receive transfer credit for classes at another university, but only a maximum total of 45 quarter units of transfer credit units  will be credited by Stanford  (including any AP and IB credits and any outside credits previously transferred).  You must get approval from your undergraduate Advising Director to take courses while away; if approval is granted, you must submit a transfer credit form to the Registrar with the course syllabus and identify the matching Stanford course. 
 
You can try to scheme out what this might mean for various options for Canady. One year away to cash in the $ and then return for her senior year might be possible, but I’m skeptical that she’d get approval to become a full-time student at another university to play basketball, even for a year, on a LOA. Why not take those courses at Stanford? I doubt that the dean of students (and the athletic department) would be in favor of a LOA to play for the other school! But who knows? 
 
I doubt Stanford would give her approval to graduate with a degree from another university—counting her Stanford credits as transfer units—after two years, then return, take 45 units at Stanford, and get a Stanford degree too. She’d have to stop short of graduating from the other university, get up to 45 units of transfer credit, and complete the required 180 units at Stanford (along with meeting the major's requirements--I saw somewhere that if you've already declared a major when applying for a LOA, you should or have to consult with the major department about what they will require of you to satisfy the major's requirements). But spending 2 years away would require getting approval to extend the LOA for a second year.

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 Stanford will often not accept units earned elsewhere because they are not "equivalent" This is in fact true with most universities. There is therefore often a "penalty" for earning units at multiple schools. In many cases it is arguably just a way for some schools to make more money.  A non-transfer student must complete a minimum of 135 units at Stanford to graduate, 3/4 of the 180 unit minimum. If someone is "returning" to Stanford (not transferring) presumably the 135 unit minimum would apply.

That is correct.

I have some family experience with that "penalty" for transferring outside course credit. While my daughter was an undergraduate elsewhere, she took a year of Organic Chemistry at Stanford one summer (along with many Stanford undergrads) so that she could study overseas for one semester (too many one-year courses required for med school to permit that otherwise). When her university reviewed the detailed Stanford syllabus for that organic chemistry course, it determined that one lecture that was part of her school's course was not included in Stanford's, so it granted her 7.8 semester units of credit instead of the full 8! I had no idea how microscopically the university would scrutinize outside classes for comparable content! Since a full year of Organic Chemistry is required by most med schools, this caused us some consternation until we realized that what's on Stanford's transcript would be what the med schools would be looking at, not what credit her own school granted.

[oldalum]

I looked up some facts to clarify the return policy.
 
To leave, you need to apply for an official Leave of Absence. If you leave without a LOA, or if you have a LOA but do not return after you have used up the maximum total of 8 quarters of LOA that are allowed, you will formally become a “Discontinued” student and the University is not obliged to reinstate you (you have to apply for reinstatement, and the bases for that decision are not given). A LOA requires approval by “your undergraduate Advising Director” and by the Dean of Students Office. (I do not know how restrictive those approvals are, but I would guess they have been mostly if not completely permissive). A LOA can be for up to one year, but then you can apply for an additional year (again I do not know how restrictive they are on granting these).
 
While on a LOA, you can receive transfer credit for classes at another university, but only a maximum total of 45 quarter units of transfer credit units  will be credited by Stanford  (including any AP and IB credits and any outside credits previously transferred).  You must get approval from your undergraduate Advising Director to take courses while away; if approval is granted, you must submit a transfer credit form to the Registrar with the course syllabus and identify the matching Stanford course. 
 
You can try to scheme out what this might mean for various options for Canady. One year away to cash in the $ and then return for her senior year might be possible, but I’m skeptical that she’d get approval to become a full-time student at another university to play basketball, even for a year, on a LOA. Why not take those courses at Stanford? I doubt that the dean of students (and the athletic department) would be in favor of a LOA to play for the other school! But who knows? 
 
I doubt Stanford would give her approval to graduate with a degree from another university—counting her Stanford credits as transfer units—after two years, then return, take 45 units at Stanford, and get a Stanford degree too. She’d have to stop short of graduating from the other university, get up to 45 units of transfer credit, and complete the required 180 units at Stanford (along with meeting the major's requirements--I saw somewhere that if you've already declared a major when applying for a LOA, you should or have to consult with the major department about what they will require of you to satisfy the major's requirements). But spending 2 years away would require getting approval to extend the LOA for a second year.

---

 Stanford will often not accept units earned elsewhere because they are not "equivalent" This is in fact true with most universities. There is therefore often a "penalty" for earning units at multiple schools. In many cases it is arguably just a way for some schools to make more money.  A non-transfer student must complete a minimum of 135 units at Stanford to graduate, 3/4 of the 180 unit minimum. If someone is "returning" to Stanford (not transferring) presumably the 135 unit minimum would apply.

That is correct.

I have some family experience with that "penalty" for transferring outside course credit. While my daughter was an undergraduate elsewhere, she took a year of Organic Chemistry at Stanford one summer (along with many Stanford undergrads) so that she could study overseas for one semester (too many one-year courses required for med school to permit that otherwise). When her university reviewed the detailed Stanford syllabus for that organic chemistry course, it determined that one lecture that was part of her school's course was not included in Stanford's, so it granted her 7.8 semester units of credit instead of the full 8! I had no idea how microscopically the university would scrutinize outside classes for comparable content! Since a full year of Organic Chemistry is required by most med schools, this caused us some consternation until we realized that what's on Stanford's transcript would be what the med schools would be looking at, not what credit her own school granted.