Getting your adoptive child to call you mom

We did the foster/adopt to a 12 year old girl and said she could call us by our first names. After living with us a year, and being adopted now for 6 months, she mainly calls us by our first names when getting our attention. She sometimes calls me Mommy, when she's feeling good and usually acting about 3-5 years old. She refers to us as her mom and dad or our first names when talking to others. I'm concentrating on calling my husband "daddy" when talking to her, hoping to reinforce a change. It leads to questions from others when they don't hear her calling us mom and dad but she handles it well. Although I would prefer that she call us mom and dad, she's been moved around so much that I'm guessing mom and dad have a lot of bad feelings around them. My feeling is that if we had originally asked her to call us "Mama ______", it would be easier to make the change. I agree it gives me a warm fuzzy when she calls me mommy now but my husband and I are trying to reinforce group hugs, goodnight kisses and other things that help US feel good.