Don't discount all 40 inch rides. My 4 yo's favorite in all of WDW is Soarin. That is followed closely by Stitch's Great Escape and some days Splash Mountain -- all 40 " rides. She also LOVES Barnstormer (a 38" ride, I believe). Just follow her lead, and trust your instincts. For example, my dd hates to get wet on the rides; so as long as I hug her to block the water on the big Splash Mountain drop, she loves it -- and then laughs at how wet mommy got.
Have fun.

Eva