Alternatively, I suggest you call a band meeting without the female vocalist and come to an agreement on what to do.
I suggest you don't call the mom out after a gig, when everyone is tired and wanting to go home. IME/IMO, that will be a train wreck of a meeting.

Expect lots of shouting and hurt feelings with no resolution.
IMO, the mom is a "stage mom", wanting to be in control of her daughter's "career". She wont' stop after the girl turns 18. Best bet is, as was posted earlier, to replace her or go on without a female singer, just readjust your set list.
You never know what your bandmates really want to do until you get together and ask them. Put up a white board and list all the pros/cons. Seems to me you can make a good case for dumping the girl more than you can to keep the mom from being involved.
I suspect that the mom will force her daughter to quit the band if you tell her to stop bugging everyone.