Update: the mare is now barefoot and I bought her a Hay Pillow, without checking back here for pros and cons. I am kind of regretting it now. It got used for the first time today in her paddock. It only has 1 inch holes because she is a hay hoover. She got a few mouthfuls of hay out, and then got frustrated. When I left the barn, it was about 25 feet from where it had been but I have no idea what she did to move it. She was wandering around her paddock looking for grass (there is almost none). But barn manager texted me to let me know that by the next hay feeding, she had eaten 90% of the hay in it.
I need a second ground hay feeder and am not sure what to use, It will go in her stall. The stall is 12 by 12 and sheās a small horse, and very neat, so I am not too worried about hay getting dirty. Just need something easy for the barn staff to use. We could try her old NibbleNet with enough clips to keep it closed, I guess.