I'm not a mom, but I am the daughter of two parents who had a lot of trouble letting go when I went to college. My folks fought me on everything from joining a sorority to religion to dating (they wanted me to have a doctorate before I ever dated
).
A lot of parents have trouble making the transition from "I'm the mother/father and you will do as I say!" to "I really don't think that doing X is a good idea, and here's why, but it's ultimately your decision."
For a while, my parents and I did the "don't ask, don't tell" thing. What finally worked, though, was a firm, "I am 21 years old. I am an adult and I have been an adult for over three years. I really do appreciate the advice you give me. But, ultimately, I have to make my own decisions in life, and sometimes I'm going to make a decision that you disagree with, but it's what I feel is the right choice for me, and if I'm wrong, I will accept the consequences.
This is my life, not yours."
Maybe it's time for this NM to sit down with her mother and have a similar conversation. Today it's the sorority; tomorrow it will be a job, or relocating to a new city, or going to grad school, or getting married. Hopefully it won't take her 3+ years to work up to this conversation like it did for me.
A dark thought: Is the NM's mom holding money over her head, i.e., "Do as I say or I'm not paying your tuition" ?
ETA: I've just seen your post that this NM lives at home. I must agree with Lindz - she must move out, otherwise she will never learn to be an independent young woman and will remain mommy's little girl.