I had the same problems some time ago with Amiro. I stopped for some time with using treats, but started with them again after some months as an extra motivation.
For me I notice that when my timing is bad Amiro starts begging. When he begs (doesn't matter if he is doing a good exercises at the same time) he will never receive a food treat. Only if he is not focussed on a treat, maybe he does not expect a treat, he get one. If he shows one sign of wanting them they stay in my pocket and all begging behaviour he shows is completely ignored.
Another handy thing for us is to not use food treats all the time. There are so many more ways to reward! For example stroking, scratching, for Amiro also leg lifts since he loves them, playing, voice reward, etc. Using food treats is only one way out of very many others to reward, and I only use a food treat like 3 or 4 times during one session. Although things also go very well without food treats
Just try to put the food away when she shows the smallest sign of begging. Do not punish or get angry, just do not use the food. I know how difficult it is when she performs a great exercise while begging (one of Amiro's a year or so ago) to not reward with a food treat, but it really helps!
For me personally I do not work very much with food. I am a little afraid that a horse will start to do things just for the treat and not because of the fun or because of communication. I am a bit scared I can not work so well with them, but in very small amounts they can be very useful and make things more fun.