This is a question less of IF I should break off a friendship, but rather what the best route would be.
I'm "friends" with a co-worker. We'd known/known of each other for about six months, and for about the last three months we've hung out together.
just forget her. ignore her and she'll go away. sounds like you've got things figured out! good job!
You could go on ignoring her, but if you feel you should tell her something tell her just what you said here:
"she is just too immature and self-absorbed to GIVE a friendship in return."
Hit it and quit it
If you don't want to hurt her feelings then stop talking to her gradually. Go from every day to every other day, then every third day. Then once a week, and so on. Do this till you don't talk to her anymore. The problem is that you work together so you have to be in contact.
Is she hot?