Stepmom support

Ive been with bf/fiance for 5 years. Ive known his daughter since she was months old. We have always been able to have a schedule for her to come over. About 7 months ago bm increased the time by an extra day a week. The schedule before that was eoweekend nd Tuesdays. Never any co visitation schedule all just verbally agreed on.. now she sed she filed for custody nd wants him to only have eoweekend.. that is a dramatic cut nd we arent ok with that. Me nd bf nd his house have been the most stable thing in his daughters life cuz mom is crazy nd narcissistic. Im having a hard time accepting that if it goes to court it could end up in her favor nd that we just have to suffer the consequences. We love daughter very much nd want as much time as her mom gets even tho her mom is never around on her time. Any advice or support?