The B2 is multiple entries

The B-2 is a multiple entries visa, which means it will be valid until it expires. My question is:

Even if it is a multiple entries visa, what will happen if she applies for a F-2 and get rejected.

The reason why we do not want to change status here is that, based on the experiences of others, changing status from B2 to F1/F2 within U.S is very likely to cause trouble when my wife needs to go out of the country and apply for a F-2 to re-entry. Many this kind of applications were rejected, probably because visa officer would consider such status change within U.S as an indication of immigration tendency.

Thank you.