Sure, but like I said, she never tried to do anything after realising (?) her mistake. She was used only up to the point when she opened the gate. After that she was willingly cooperating because that's also where her instructions probably ended, and, like you said, Biba didn't really care if she comes back or not. Though I'm sure Biba is more than happy to keep her around to serve as the core of another abomination, should the need arise.

To be honest I expect Mumei to seemingly redeem herself by freeing Ikoma later, or something along those lines, but in my current mindset I'd prefer her to lose her mind and turn into a monster in the middle of an aggregate.