You can buy trainers with hidden heels in but the cm will probably tell your child to take their shoes off if they spot them.
https://disneyworld.disney.go.com/faq/parks/restricted-personal-items/
You may not bring the following types of items into the theme parks:
.....
Shoes with built-in wheels
The best way to get an under-height child on a ride is to wait until that child is *honestly* tall enough.
I know I will be cursed by some for bringing this topic up. If a child will be an inch too short at the time of trip (for certain rides) what is the best way to gain that extra 1/2-1 inch needed to ride? I get the safety concerns and all and not looking for a lecture on the topic. I am sure I am not the only one to come across this and I am sure some have found ways to get the extra height needed and survived to tell the tale.
Is she under-height in shoes or out of shoes? If out of shoes, remember that she'll be wearing shoes in the parks. So measure her in her comfy shoes.
But listen...even if she hits the mark wearing shoes, if she's close, you almost certainly will end up in a situation where she could ride THAT ride, but couldn't ride that other ride. Because the very forces she is encountering on the bigger rides are compressing her spine (and yours and everyone else's). So you are going to have to prepare her and yourself and other family members for the very likely possibility that she will have to miss some rides.
If she is barely at the mark wearing comfy shoes that aren't going to hurt her, make sure she's getting more than enough sleep, really good hydration, and isn't slouching. Hit the MUST DO ride very very first thing in the morning, and expect that she might not hit that same mark the rest of the day.
With a borderline child (and if she's being measured barefoot she might very well be borderline with normal shoes on, which is why I'm answering) you have to have that possibility in mind. CMs who think she's underheight are totally allowed to even slip a piece of paper between her head and the height stick. If the paper goes through, she's NOT getting on.
So not only does she need to be tall enough, she needs to be mature enough to know what she needs to do (stand straight and tall, try to touch the bottom of the stick with the top of the head, dont' let there be ANY space between head and stick!) as well.