Daughter turns 3 in july. Speech delayed. Only says 7 8 words. But understands everything. Slp evaluated her. Not autistic. Very smart. Common?

May need help. It is excellent that your daughter is not autistic, but expressive language disorders are quite common and can be frustratiing for chlid and parent alike. Although, as dr. Dreyer noted, language not infrequently kicks in spontaneously (especially if family history of delayed speech), it would not hurt to work with an slp to see if communicatoin can be facilitated in some way, even sign language.
Delayed speech. This can occur fairly frequently. You say that she has been evaluated. Has she any other delays? Some of the reasons can be that you anticipate all her wishes and she doesn't have to talk. I assume her hearing has been tested. If this is normal it could be she just doesn't want to or has no reason. If all the evaluations are normal relax my son din't talk until after 3 and he has iq162.