I haven't read this whole thread, but I just wanted to chime in here -- apologies if I'm being redundant with what someone else has said.
My son will be 7 on June 6 and is 42 inches, so we have struggled through this, as well. And I will validate that children, especially astute, intelligent children, are very aware of the height difference, and it can be very discouraging and frustrating to them.
Our situation is a little different, because we live near Disney World and go 2X per year for an overnight visit, but perhaps you can get some mileage from the approach I have used with my son.
* Expectation setting up front -- when he was right about at the cut-off, I made sure I knew all of the height restrictions on the rides, and I would warn him before he got measured for a particular ride that he may or may not be able to ride. I didn't broach the subject in terms of age, b/c that isn't really the relevant issue, and he didn't seem aware that younger children were riding. And if he didn't ride, I didn't ride.
* Expectation setting for future visits -- "It will be fun to have things that are new and exciting to ride on your next trip".
* Encourage repeat riding of favorites. When my son was around four, he wanted to go back again and again to his favorite rides and it was actually difficult to get him on something new. If you find this is the case with your daughter, use it to your advantage! We get a ton of mileage out of Goofy Barnstormer and Tomorrowland Speedway.
Relax!! There is plenty to do, even for the "short set", and you will all have a great time!
Have a wonderful trip!