Did she let the embassy know that she has this intention to change to student visa? I think, there are some note that they put on the visa stamp, saying you intend to go to student visa.

If not, then it is tough. USCIS would not take it favorably when a visitor tries to change the visa to student in USA itself. It wants any applicant to go through the whole process in their own home country, I think just to make sure you have the integrity to study and learn more in your field. If visitor visaholder tries to do this, the general feeling to USCIS is that there is an intention to immigrate later in future, which they do not prefer.

That's the kind of paradoxes we have to live in this country we call as United States of A. You might stay in here for 10 years in student visa and get married and make babies, but you should never intend to immigrate at least in papers! But my saying may not hold true all the time, some people go through this process without any problems, I am just telling you what I studied at one point of my life.