A horse generally need its teeth floated about every 6 months to a year, so if it's been over a year, than definitely give the vet a call.
Anyways, not eating hay is not normally a sign of a horse needing its teeth floated, but I could be. It's possible that your horse isn't eating his hay because she I still getting used to the new place. Did you feed her her hay in a net or on the floor? How does this place feed her? If she still isn't eating her hay, than try to feed her alfalfa cubes. Put them in a bucket and put warm water in the bucket. Mash the food together and tadaa! It might be more interesting for her to eat that way. Good luck!
P.S. If this continues, call a vet ;)