No way la, she is your hubby's mom and hence your 99.
It doesn't matter the way you call her as you know her very well now. Take the name itself as just pronounciation, not the meaning. Be generous, at least superficially.
If your 99 treated you very well at the beginning, this means she is not that bad but just be influenced, indoctrinated... + she has been long looking forward to a grandchild and lost independent thinking. Someone is very good at taking advantages on her pregnancy.