Congrats, Amy! I know that is a wonderful feeling. Lilia (age 2) has started to call me Mama too.
It is SO fun to hear!!
Regina (age 4) has been calling me Mom or Mommy for about 6 weeks but unfortunately she also calls people like my hairdresser "mom" or a random stranger in the McDonald's playland "daddy". I definitely think she knows I am her main caregiver but she doesn't understand the exclusive use of the term. So I've been teaching her she has ONE mommy and ONE daddy and showing pictures of others or me and saying "Is that your mommy?" Seems to be working. The language barrier is so tough on stuff like this.
Ok--sorry I got off on my own tangent. Enjoy your talking daughter!