Sorry to ask you, is she in Nepal or in USA already? Because I was talking about the one who is in here already with the visitor visa.

If the case is like that where the visa holder is in USA already, then it might pose some complications like I talked about previously. But, if she is in Nepal and recently got the visitor visa, then, I think it will not be so advisable to change to student visa right away after getting the visitor visa, as it just shows that she is not prepared and she might immigrate with such indecisiveness about which visa to procure. If she has the visitor visa recently, and wanna change it to student, then may be she should give herself some time, forsake plans to travel right away and apply for student visa later on, for next semester may be. I hope that helps, that's my best suggestion, I may be wrong though.