Could my infant daughter be showing early signs of autism?

I am a mom of three, a two year old daughter, and 3 month old boy-girl twins.

I gave birth to my twins by c-section on 9-18-12, exactly one month early because I was dilating too early and my daughter was breech against my cervix and she was at risk for coming out leg first. They spent no time in NICU and went home three days later.

They are just about three months now and my son is cooing and making noises, "talking " as we put it, smiling, and generally just seems like the happiest little boy with such personality and sense of humor. His twin sister on the other hand is the opposite. She rarely smiles or makes eye contact. She maybe looks at me one time for a couple seconds every day but most of the time is looking over her left shoulder. If I turn her, she looks over the right shoulder. This child will go out of her way to avoid looking at us! To the point where if we keep pressing it, she gets angry and cries. I don't understand why she is like this and it's scaring me that she may be showing early signs of autism. She eats and sleeps normally, sucks her hands, her hearing is fine as she responds to noises and when her dad gets up in the afternoon (he works nights) she looks around when she can hear his voice in the room. But when we actually pick her up, she doesn't want to smile or even look at us. She just wants to look at the ceiling fan, christmas tree, or she LOVES the tv. Sometimes the ceiling is more entertaining than us. Could she just be a little slow due to being born early? But why is her brother doing all these things and she isn't? I'm very worried and I've been working with her constantly and every time I can get her to look at me, I go out of my way to keep her attention for as long as I can, which isn't very long. They have a doctor's appointment coming up at the end of January and I plan on asking her about it then. What are your thoughts?