Sharon has always been a terrible mother, who uses her kids to get what she wants. I remember very clearly how she chose Adam, knowing what he did to Faith and how she left her kids to help him or "find herself". Christian wouldn't remember being with her and Dylan so she's not the only mother he knows. He was still an infant when Nick took him and she wasn't part of his life until Nick moved in. Didn't Nick tell Chelsea she was his mother .
I think Faith is an obnoxious , spoiled brat but she's the only one of Sharon's kids who called her out over Christian. Mariah kept her secret while they both whined and pretended to feel guilt over hurting Dylan and Nick. Noah refused to let her play the victim card when she knew the truth and kept quiet, but expected her to be forgiven and pitied , enabling her as always. Faith felt sorry for the ones who deserved it, her father and Dylan, not Sharon, and then moved un with Nick. Sharon doesn't care how her actions affect Faith, she uses her to guilt others into keeping quiet.
Faith knows that her parents are better as friends and this reunion won't work.