I would talk to the whoever is looking after your baby. See if there is something that causes her to do that or one particular baby. Also, they might have some suggestions.

Is she aggressive at home as well? If not maybe there are different situations when she´s together with other children that triggers it. How old is she? Is she old enough to talk to? Maybe you could join her for some days and se what happends then, just to observe how she acts in the group.