When someone gives an ultimatum of “me or them” (a or b), the best choice is almost always never a. It is the least restrictive choice.

If there were an actual reason to not choose b, the best choice is likely neither.

I understand the argument that “she is struggling” but the moment they make their struggle your struggle they are choosing to spread the pain rather than deal with it. This is never acceptable in a parent child relationship, more so if the child is a minor.