she even covered for me at times.
Think about this statement. She covered for you, and you don't know the answer of whether she is a friend of your marriage?
I cut those people from my life as well. I believe that there were good intentions, but the encouragement to do what it takes to make me happy was misguided. I'm not safe, so they aren't safe. I want friends who encourage me to talk to my BH. Not friends who "cover" for me. Real friends call you out when you are doing something wrong.
Is she a real friend to you? Maybe. Is she a friend of your marriage? No way.