Give it time and she'll get over it... or not, but you can't control the after math. You both made mistakes, best just to move on. You were the middleman in your boyfriend's and your friend's bullshit, never a good place to be.

No it wasn't your fault, you tried to explain why. Even though you should not have had to. It was your birthday plans that you decided to invite her to. Happy birthday by the way. If she can not understand your reasons then oh well. Friendship is great but there are some boundaries that should be respected. Sorry you spent your birthday upset anyways.

I think it was mostly her fault cuz she invited someone to come along even after you had already told her no that it wouldn't be a good idea. Whatever the reason you didn't want that particular friend to come along shouldn't even matter. It was your plans and your birthday. Happy Birthday by the way!!!!! I say just give it some time and everything should cool down. I am kinda going through the same thing. Hope everything gets better. If not, it is what it is and you can't change the past. Hopefully the future will be better for ya. I'd give you a nice big hug if I was there and it would help.