I think Molly Fyde is a much easier and accessible book for a 10 year old. That series may meet with more success. I can see how it would also make a more empathetic read; especially when you take into account the female heroine.
I agree, that she would probably be fine reading Wool, but understanding some of the deeper meanings and metaphors may be more difficult. I grew up in a house where everything was a pun, metaphor or analogy, so it's hard for me to gauge. However, I think with a well led discussion, and properly directed questions, she could probably be taught to appreciate the nuances of the story. It may even open her eyes further to the use of double meanings and common threads/ themes throughout a book.