I don't suppose there is more than one Nursery? Our new ward has three, and I know that's not the norm. But another ward I visited had two nurseries. They have a little blind boy who can't tolerate the sensory overload of rowdy children, so they've actually split their two nurseries by noise level. Funny, huh? They asked me if my 2 year old was quiet or loud. That was easy! We sent him to the loud class. I feel sorry for the teachers in that class, but I thought it was a marvelous idea. If you have more than one nursery, talk to the nursery coordinator and suggest that idea. Or if you only have one, you could talk to the nursery leader and see what she thinks of splitting up the class for a half an hour or so, by pulling the curtain closed. The more rambunctious children could do suitable activity, and the quieter children could do a quiet activity. Even if you just did that for a week or two, you would see how your daughter does in a calmer situation. If she is willing when the class is quiet, you know that you've hit on her issue, and maybe the Nursery leader would be willing to continue that schedule until your daughter has adjusted a little better.
I was a nursery leader, and I don't know if all of them feel the same way, but I think they have the responsibility to help children transition from babies into Sunbeams--children who can happily go to class, obey their teacher, and sit still through a short lesson. If that's how your nursery leader feels, she'll try to do what's necessary to help your daughter be happy in nursery.
Also, I'm guessing that with just you and her at home, it's pretty quiet around your house. I don't have that problem with two boys! I think it might help to expose her to crowds. Take her to the Mall, the park, anywhere that is kind of loud and busy. When she starts to get upset, you can leave, but it should take longer for her to get upset each time you go. I dunno, it seems like it ought to work!
Good luck!