I have taken my 12 year old to see The Lion King, Chicago, Les Mis, Joseph (tour not West End)Wicked, Billy Elliot and Mary Poppins and Grease. She loved them all and is now desperate to see Hairspray!
Wicked is definately not too young for her - it is very clever and the music is fantastic! One of the best shows I have ever seen a really awesome experience.
A cautionary note re Billy Elliot as the language is shocking at times.
My dd adored Les mis - and still does. If you chose that one I would explain the story line to her first and take plenty of tissues with you.
Whatever you go and see, children always seem to enjoy it more if they recognise the music. We usually buy the OCR when we order the tickets! Enjoy!