Both my sons were speech delayed. DS2.5 still is but DS4 didn't start speaking till he was about 2 years 9 months so still waiting to hit that milestone with DS2.5. DS4 had 10 words total at 24 months ... 9 months later he suddenly started talking in full sentences. He just turned 4 and won't keep his mouth shut! lol ... DS2.5 was even slower, had maybe 6 words at 24 months (including mommy and daddy) ... but aside from the 6 words could count and recognize the numbers to 20 and backwards from 10-0, recognized the whole upper and lower case alphabet, and his first words he learned from then on were all the basic colors and shapes ... but not many useful words for a daily life. He's just not interested. He doesn't talk really unless he's pointing to animals or things naming them (now at 2.5) ... yet we went to the doctor's office and suddenly he stands up in his stroller and says with perfect pronunciation "Let me out!!!" ... I was floored! lol ... and things like that that happened before. He won't do single words or two words but suddenly blurs out a whole phrase. ... so very asynchronous.
Both have speech therapy but DS4 doesn't really need it. We just keep him there to have our foot in the door for Special ed in the school district. DS2.5 get speech therapy through early intervention but we're not really worried about the speech. His brain clearly works fine, he's just not interested in speaking for the moment.
I'd have your DD evaluated by Early Intervention if you're concerned, and most likely you'll get their services (sounds like she might have some sensory sensibilities too?) ... but yes, it's possible to have a gifted child who's speech delayed.
Oh, and I almost forgot ... DS2.5 now has a vocabulary of probably 100-150 words he says ... and has been able to READ about 2/3 of those words the last 2 months! (words like octopus, tiger, zebra ... not just cat, hat, etc. simple sight words) When I tell someone he's speech delayed and reading, they usually laugh into my face!
