In her case, it would be quite difficult to show that she intends to return (for the F1 case), as she would be indicating that she has a fiance in the US. My guess is that they might deny her an F1 based on this. Perhaps it depends on how you portray your relationship. Perhaps you could think of your relationship as a significant-other type, and not fiance-fiancee type one, in which case she wouldnt have to mention about you in the F1 application. That way she would have a much betterr chance of getting the F1. But if you are at a later stage going to claim the finace-fiancee relationship (for a K1, which you may not need if she gets the F1?), then they might ask how long you have known each other, how you met etc. That might be important even to show that your subsequent marriage was legitimate (if you intend to marry soon). Denial of F1 due to immigrant intent might be better than denial (of K1) due to concealing facts. So the proper course of action would depend on many things, especially timing of her application(s), how you think of the relationship, time of subsequent marriage etc.
One course of action could be: portray your relationship not as a fiance-type one, apply for an F1. If she gets it, then she comes to the US, and you take it from there, noting that you cannot suddenly change your relationship to the finace-type. If her F1 is rejected, wait for a few months and try for the K1 properly, at which time you have to provide reasons that your relationship became stronger since the time of last denial etc...
Regarding type of school, how good a student, it might help to be in a good school and be a good student, as that might be helpful in convincing that she intended to study, and not coming to just immigrate eventually. A return ticket, strong family ties, parents and siblings in India, possible job prospects etc., how her educatiuon might help her career prospects in India etc. all might help in getting F1 visa.
Also search more on the requirement for K1 (see the other forums),as I think K1 is for people intending to get married within a certain time of coming to US.
Not legal advice, but good luck.