I don’t think Magic Treehouse is too little kid. It all depends on what your daughter likes.
Flat Stanley
Wayside School by Louis Sachar
McBroom books by Sid Fleischman
Encyclopedia Brown
Cam Jamsen
Nancy Drew Notebooks/Nancy Drew and the Clue Crew
Secrets of Droon
Where the Sidewalk Ends (quirky poetry)
I’ve heard great things about the Scholastic Branches books. My kids are older and these weren’t available when they were young, but I think these series are supposed to be good for kids who are about that level.
https://www.scholastic.com/site/branches.html#promo
The Princess in Black series is somewhat “little kid”, but really well done. They might be good books that she could transition into reading by herself.
Books that are more on the challenging side, but might work for shared reading a little later on:
Princess Tales by Gail Carson Levine
Mrs. Piggle-Wiggle
Boxcar Children
Beverly Cleary