you can be polite about it, but you have to tell her "look, you have to talk to me, you have to tell me what you want, i have to tell you what i want, and we have to work out what makes us both happy." because the bottom line is, you know you won't be happy with just a second person tagging along with you forever. Your girlfriend is very young and is taking your lead.
She will listen to her mother and to you before she will listen to her own heart.
My question is this: even though she is the one that wants to spend the night together most of the nights and seems to want to be with me, why would she randomly start caring what her mom thinks?
Is she using her mom as an excuse because she is losing interest? I am starting to believe that anything she says is hard to believe now. just broke up with my gf over similar issues, amongst other things.
Some background: She is 20 (sophomore) and I am 23 (senior).