My oldest was similar, reached milestones very early, talked early and everything else. Yet he was extremely hyperactive and 'odd'. Have you noticed anything else she does? My son was diagnosed at age 3 as high functioning autism. To everyone else, he looks and acts normal. But then they hear him talk about things he's interested in, he can't hold a conversation, has fears and obsessions and lots of sensory problems. And he's SO loud! Yet he can't handle noise. Go figure! What you need to do is speak to a Dr or do a google search on ADHD and autism. They go hand in hand.
My son would line toys up. He wouldn't play with regular toys. He'd use household items and things. He could recite his alphabet and numbers before he was 1 ! He was soooo clever. I thought he was just a hyperactive little einstein..lol. But as he got older, I noticed more odd behaviour. He screamed all the time for no reason. He never slept, not even naps. And during the night I was up EVERY hour with him. This only started waning when he was about 4yrs old.
Just keep watch of her, and monitor things she does. Maybe keep a little diary. Does she have trouble with sensory issues? Sound, touch, sight etc? My son cannot stand being wet, having mess anywhere on him, fluff and taking his shoes off. He can't stand loud noise, though is very loud himself. He is obsessive with certain subjects of interest. He watches dvds over and over and has frequent meltdowns. Yet he's so happy and lovable. Everyone he meets loves him. His hyperactivity didn't wane until he was over 3yrs old.
Btw, my son is VERY social. He talks constantly, loves attention and being in peoples company. The difference being is that his behaviour isn't always socially appropriate. That is where every autistic child differs. Some prefer to be alone. Others prefer to be with people, but on their own. And some like being with people but only talking and doing things that interest them.