I figured out what she is doing!
Every time before we go to sleep I sing the same 4 songs. Lately she will sit so still while I'm singing that I think she's asleep. Today she started singing with me! When I would start she would start, and when I finished a song she would pause and then sing a few notes as if to say "One more time mommy!"
My heart just melted- And we sang for a MUCH longer time than usual...