I'll give it a shot....

Seems to me that perhaps cutting your hair, especially in the front which outlines your face, may possibly represent your need of exposing who you ARE, and with your mother included in the dream, maybe that signifies that you are seeking her acceptance...exposing your REAL self to her.

Disgarding your hair in the trash may mean that you are intently disgarding what you've been hiding from, (maybe past, or what other's, or self, thinks of you).

Your mom's disapproval and reminding you that you wouldn't be happy with your choice of "exposure" of self may either represent your fear of mom's present disproval, or fear of sense of failure.
You not being able to "do" anything with your hair afterwards may represent possible confirmation of mother's disappointment, or your own of self...resulting in mother actually stating to you.

And, the fact that you didn't care if she chastised you may represent your acceptance of your present misery? Not sure on that.....though...I'm not sure on any of my evaluation.....Just my perception of what it all MAY mean?

This is sorta fun....lol. (You should hear my most recent dream...lol..in fact, I think I'll post it, as well...Talk about bizarre...and quite long).

Hope that helps a bit.

Shangrala