DD7 enjoyed some of the Paddington Bear series. They're safe yet written in a more sophisticated writing style. According to Lexile.com, "Paddington at Large" is intended for ages 3-8 but has a Lexile score of 1160, or about a 9th-grade reading level. I remember her laughing out loud a couple of times, which is always a good sign.

Stuart Little was another safe book she liked.