She sounds a right selfish cow by the sounds of things. What about all your other friends you would have ended up inconveniencing if you had changed your birthday venue?
I too have the odd friend who I end up doing most of the running for, if I want to catch up with them then I will get in touch but they rarely if ever get in touch with me. I stopped bothering a while back though. Life's too short. Try chucking some of her excuses in her direction, give her a taste of her own medicine, she might get the hint then
As for the whole parents/friends thing, tell 'em to get stuffed, you choose your own mates and thankfully you're an intelligent lass who can no doubt pick em well...I'm one so you must be