L.A.
I know it just sounds awful and you are feeling bad, but keep this in mind.. A teacher told us this advice in Kindergarten "You believe 50% of what your child tells you goes on in school, and I will believe 50% of what your child tells me goes on at home. "
Just speak with the teacher.
My guess is that maybe once the children did not play with her.. or they did not play the way she wanted or something else.. But I would really, really doubt that NO child would play with your daughter.. It just does not sound like pre school kids.
Just breath and continue to advise your child to be kind, to ask to share, to ask to join in and then to remember to allow others to join her when they ask..
This is all part of preschool.. They are just learning social rules..