you did not say how old your daughter is but here is my advice-
I don't know how you feel about dating in general, but it is unbiblical and in my house at least, our girls know where we stand on it and why- they have been given good foundational teachings about the purpose of dating, worldly dating versus biblical courting and the consequences of it all. My oldest who is 15 and has been asked out, has a good head on her shoulders and says she is nowhere near ready to be married so dating holds no attraction for her- she does not want the emotional baggage that comes with no blessing or benefit. So though I believe homosexuality to be wrong, the same goes for this kind of relationship at this age- it is inappropriate whether it be a boy or a girl.
Second, your child is still in your home- you have the right to control the influences she is under. If my daughters have friends that encourage disrespect and defiance when it comes to authority, these friends are spoken to about it and then if there is no change, it is cut off. My oldest is now mature enough to make these choices on her own- if she is friends with someone who is walking a path she does not want to walk- she will choose to invest less time in that relationship and more time where it is profitable. Your daughter is still under your God given authority- if she is making poor choices regarding friends and fellowship, it is up to you to step in and put up some fences.
You need to sit down and talk to her and reiterate- no matter how she thinks she feels about this person (whether it was a boy or girl) the most important thing is that she and the other girl show respect for your authority. Is this girl going to provide for your daughter what you provide for her- food , shelter, clothing, etc? No, she cannot, she is unable to in every sense of the word. Her only motivation right now is to stir up rebellion and disorder. You are the authority in your home and you are responsible for order.
All this "accept her for who she is" is nothing more than a tearing down of your authority and God's order. When she is out of your home and wants to pursue that path, then it will be between her and God and she will have to deal with the consequences - and that is for whatever kind of relationship she decided to pursue- if it was a guy disresecting your authority it would be the same answer.
This girl does not care enough about your daughter as she has made your daughter believe because she does not care to acknowledge your role in your daughters life- she has no concept of resonsibility, honor and respect and though your daughter may be angry for a time- you cannot expect her to make a right choice here and you have every right to make it for her until she either changes her attitude or she is able to provide for herself.
I will pray for wisdom and discernment for you and for your daughter and that your daughter would no longer be prey for this other girl, that she would seek after God's blessings by honoring and obeying her parents and that your mother - daughter bond be strengthened and this false relationship would dissolve quickly.
God Bless you and your family