You are confusing the age of consent with the age of majority.
Until your girlfriend reaches the age of 18, regardless of the age of consent in your state, what mom says goes. If mom says she doesn't see you any more, then she doesn't see you any more. Doesn't matter one whit whether she accepted it before; NOW she says no. That means it's no.
When your g/f is 18, she can do whatever she likes. Until that time, Mom and Dad have 100% say as to who she can see, what she can do, and where and with whom she can do it.