Better to be crucified by folks on the forum than by Immigration Officer during stokes interview!
She could come to study, she just cannot be 100% sure she will be marrying and staying in the US.
While I see your point, I do not agree with you fully.
- AOS and CR1 take about the same time nowadays.
- If AOS is from B1/B2 the beneficiary cannot work legally in the US for a while, and fully depends on the US spouse. At least the beneficiary usually can work back in their country while waiting for CR1 visa.
- Beneficiary going through AOS usually cannot travel anywhere outside of the US for some time, even for emergency. Beneficiary waiting for CR1 visa can take trips anywhere other than US (and sometimes to US) freely.
- AFAIK consular interviews are much shorter than AOS interviews at USCIS local field office.
- CR1 applicants do not have to worry about immigrant intent, whereas some AOS applicants go through increased scrutiny and have to prove they did not plan to adjust.
Of course, there's many downsides to CR1. But to suggest AOS is walk in the park and doesn't have any downside would be unfair.