My son is about to change nurseries and he's got a huge crush on a girl in his current one and is all tearful about leaving her (so cute!) but my experience is that young children change freinds very quickly, once ones out of sight a new one comes along, so I'm sure your daughter will mix in just fine.
With my girls, I've seen all of them be close to a couple of kids in nursery, then when they start a new school with new kids even with there old freinds in the same class, they all move on to new ones. So I really wouldn't worry about it, kids change freinds regularly at that age and if she's very dependent on this girl for freindship I'd see it as a healthy thing to widen her circle of freinds.