MIL Question

So hubby and I our expecting our first child in July.  This is the first grandchild on either side.  Well when we announced we we're expecting back in December my mother in-law immediately said she wanted to be called mama.  I am not ok with this as I feel that's what I should be but hubby doesn't really see the issue. My question is would you be ok with with your MIL being called mama?