What are the ages of the class she will be in? When my DS was the same age as your DD, he was in the infant room and there was no "class" schedule. He was able to nap on his own schedule. It wasn't until he moved into the toddler room (@16 months) that the whole class began to nap at the same time and at that point, he had already transitioned to just one nap, so it wasn't a huge adjustment for him.
With that being said, I will say neither of my kids have been great nappers at school. My younger DS is better than his older brother was, but he still gets about 1.5 to 2 hrs at best and comes home tired and cranky everyday. Yet, when he's home on the weekends or days I don't work, he will nap for about 3 hrs on average. Both of my boys are light sleepers and I think that is part of the problem. But all kids are different, and hopefully your DD will be a better napper than my kids are/were.