She could be feeling reluctant to eat hay because her dental might be causing her to experience some pain from eating the dried hay. Maybe because the coarseness of it hurts to chew, or it could be that her jaw is sore from her mouth being propped open for the dental procedure, so that the motion required to chew hay makes her jaw hurt. Those would be my guesses since you describe her as being excited to eat her other food. So maybe for a bit you'll need to stick with soft food until the pain has subsided.
If you have access to plenty of fresh grass, I would offer lots of that to her until she's had a little more time to recover and any soreness to go away, provided fresh grass isn't causing any digestive issues. The grass will help with the tooth wear and also keep that digestion moving. Then as the soreness fades, you'll likely start seeing her snacking on hay again. Then that would be the time to transition her back from fresh to dry hay.
If you have access to plenty of fresh grass, I would offer lots of that to her until she's had a little more time to recover and any soreness to go away, provided fresh grass isn't causing any digestive issues. The grass will help with the tooth wear and also keep that digestion moving. Then as the soreness fades, you'll likely start seeing her snacking on hay again. Then that would be the time to transition her back from fresh to dry hay.