My 11 month old acts like she doesn't know who I am?

My daughter is about to turn 11 months old. She can say "dada" "gigi" (which is my mom) "pop" (which is my stepdad) "gadada" (meaning grandaddy, who is her great grandfather) and "spongebob" Everytime I try to teach her "mama" she laughs like she is going to do it or wants down. It upsets me cause her dad isn't even around. I try asking her "Where's mommy" and she doesn't look at me or anything. I have tried using different words other than mommy like 'mama' but she still acts like she doesn't know me. Although when I say "GiGi" she looks at the door as if she knows that's where my mom will come in. It breaks my heart when she doesn't even look at me but does with everyone else. It's just me and her all day everyday, I do everything for her. Why is she acting this way?