The child behavior site might be a better site to post - unless she is on ADHD medication.
If this is a fairly recent thing it sounds like it could be due to sinus congestion. Can she breathe through her nose with her mouth closed? If she can't, then the sinuses are stopped up.Maybe allergies from spring time pollen? You might try a short acting nasal spray to open them up. They also have those nasal strips that go across the nose to help breathing. Tlhey make them for kids now. Hope this helps, but do try posting in another site.