[chuckle] Sounds like it's probably selective hearing - especially if she passed her infant hearing screen. (It amazes me how well my 14 month and 4 year old sons can do this.) When you say something she wants to hear, does she prick up. (Stuff like: Would you like a cookie? Here is some juice, etc.) If not, maybe you should make an appointment with the pediatrician to have her ears checked. It could just be that she's got too much wax in her ear canal and it's preventing the ear drum from vibrating properly.
The other day, my 4 year old was watching a movie in the other room while my hubby and I were in the kitchen making out a grocery list. I asked my hubby to put chocolate milk on the list, and my darn kid came RUNNING in all excited saying he "likes" chocolate milk. Now, this is the same child who will act as though he's hard of hearing when I am in the same room as him and ask him to go and brush his teeth!
My oldest was also pretty slow to start talking. He went from speaking a handful of words to speaking in sentences by about 2 1/2.