My 6yr old brother is very bright intellectually. He does have aspergers though and in his case his talents may be because of that. He was late to talk, but as his primary carer from 6 weeks to 2yrs I read to him a lot. He was very interested though, he had a huge stack of books and every night i'd have to read them all to him, without fail. When he did start talking when he was about 2 and a half he jumped straight into reading. I'm sure most of it was just repetitive, as he could recite cat in the hat, but he would also follow the words with his finger which made me think he at least understood the correllation between the words on the page and what he was saying. His favourite car game would be to see store signs (like Asda, Morrisons etc.) and spell out the words and then repeat them backwards e.g. A-S-D-A, A-D-S-A Asda. He's obsessed with cars and knows lots of different models and engine sizes and other random car type things that I have no clue about, but again, i'm sure it's mostly the autism in him. Not to detract from his talents at all though!
Now he's at school his reading, writing and maths skills are years ahead, but his verbal and communication skills are lagging a year or two behind, which is expected.
If she's showing such an interest, keep it going! Make reading interesting and fun, including silly noises and see where she goes from there! It definitely won't harm her!