There is a variety of subjects that for some... deeply challenge their moral/social sensibilities. The day you announced to anyone that you were bisexual brought you to a shakey place in our society. Surely you knew that...and now you will have to deal with what comes with that choice, in my opinion.
Your friend does not come across to me as being necessarilly not nice. She is well within her rights & boundries to invite whomever she chooses to her party. You can come to the party respecting the boundries she has set according to her moral /social sensibilities or you can, sadly for you, decide to take this as a "betrayal" and allow your anger to cloud the issue and possibly lose a good friend.
Imo..friendship is respecting the others' boundries...and feelings, both.
I can elaborate in another post..if this is too hard for you to digest. Take care...and don't let this drive a wedge into an otherwise good friendship?!
~Dottie