There are some simple gestures that can help her, for example start grooming her at the neck and shoulder, working your way back to the more sensitive flank regions.
you can try is giving her Banamine for pain relief. A day or two of Banamine can make a world of difference. If that doesn't work, ask your vet to examine her to make sure her ovaries are normal and to suggest any further treatment to help her.
Try to avoid picking at her, but when you ride her she has to understand that she has to work, but work on simple things for her.
You'll have to experiment to find the right combination of tasks that will keep your mare working with you without putting her into overload.
Hope it helps x