My advice would be that the next time she asks you to teach her to read that you say, "Well, what would you like to know about reading?" And just discuss as much as she likes. I would strongly recommend not starting a formal curriculum at this point. I've heard of several kids (all older than your DD) who were at a similar stage of reading readiness and similarly asking to learn to read, but who were turned off very quickly once formal lessons began--much to the frustration of their mothers. Just because they want to learn/are ready to learn doesn't mean that they are ready for lessons. While I would definitely not tell her she has to wait, you might tell her that it takes a long time to learn to read; that she already can read some words; that you are sure she'll keep learning to read more & more words all on her own; but that you are also happy to answer any questions she has.
When DD was that age and wanted to read, she was often satisfied when I let her (sight) read a word here & there as I read to her. (E.g., I would say, "You can help me read if you want to. Why don't you read the words 'frog' and 'toad' and I will read the rest of the book?")
