Dating problem?!?

my friend YES LITERALLY MY FRIEND NOT ME... is dating this boy, they have been going out for 2 1/2 years, she's a junior in high school and he is a freshman in college. her mom hates this because he is now in college and she's afraid her daughter will be pressured into "stuff" none of the aforementioned stuff has occured yet. the mother is also worried because he has told the girl that he plans to marry her. the mother wants her daughter to break up with him and experience dating other guys before she settles down so what should she do? my friend wants advice from me but this is a problem that i just cant seem to hel her with