After months of maternal ambiguity, she certainly knows that word now, and walks around constantly saying it in different ways.

Mommy--declarative (there's my mommy)
Mommy--imperative (be my mommy!)
Mommy--possessive (be MY mommy!)
Mommy--interrogative (where's my mommy?)
Mommy--interjection (mommy is a force of nature!)

Mommy--so much more than a proper name