The Betsy-Tacy books by Maude Hart Lovelace--wonderful series and starts when the girls are around 3-4 years old. The Betsy character is wonderful! There is a part in the first book where Tacy's infant sister has died, you can skip it though if you find where it is.
Junie B. Jones are fun even though Junie is a sassy little girl--my DD was quite shocked by some of her antics. She's fun to read aloud though because the character has a great voice and many altered understandings of words (pronunciation, syntax and meaning
).
Phantom Tollbooth? My kids were older when we read them, but I think it would be ok.
Mercy Watson books by Kate DiCamillo if she likes a bit of silly now and again (my kids were constantly quoting one of the characters)
It's fun reading peoples' ideas because in our house there is usually some oft-quoted line that comes immediately to mind and brings a smile on to my face. In our house oft-quoted lines tend to the silly rather than the profound