My son was a late summer birthday, and it took him until Dec of kindergarten for the light bulb to go off and for him to know all the letters and actually start reading. My daughter missed the deadline and started K when she was almost 6, but looking back, she "got" the letters and reading at exactly the same age, around 5 1/2. So don't worry too much about that right now.
As for the not answering the questions, I can think of a few things to check on:
1. how is her hearing? They wanted to hold my son back in the 3s because they said he couldn't think for himself when the teacher asked him questions or told him to do something. I would tell him to do things and he did them just fine. I was shocked to learn he couldn't hear a darn thing the teacher said to him because of fluid in his ears and would repeat the other kids or just ignore her. Once we fixed the hearing he was just fine.
2. Does the teacher make her nervous? My son is very outgoing. His first grade teacher made it her mission to make every child recite their phone number in class. We moved recently, so the phone number was new to him and not surprisingly, he didn't know it at first. We worked on it, and after getting several notes about him not knowing it, finally I wrote back that he had learned it. The next day I got a note home that I was wrong and he couldn't recite it. I pulled him aside and asked him to tell me his phone number. He said it over and over. I asked him why he wouldn't tell Mrs. G. He smiled and said she made him nervous and he forgets when she asks him. The next day I wrote her a note that he was nervous. What do you know, he could do it.
3. My nephew will selectively ignore us when we talk to him and ask him to do things. He does this at school too. When his parents tell him to do something he mostly does it. I don't know if he is shy but I think he just wants to do what he wants to do.
i really do think though that if you give your daughter some time, she will mature and do just fine.