Can you mix the old hay with the new hay? You could also put the hay in tp tubes to make it more interesting or add dried herbs to the hay to make it more appealing. What does the hay look like, is it long green strands or musty short flakey brown pieces? Does it smell fresh or moldy?
This is why I always have a stock of 4 types of hay. Then when you get a new batch they don't like it's not a disaster. Get some other hay and give her both.