Could she be trying to process what you are saying...and repeating it is giving her time to think about what you are actually saying to her. My son does that....he also has echolalia where he repeats lines from TV shows, randomly quotes people as they walk by, lyrics to songs over and over again. He has functional and non-functional echolalia. I think he repeats us because he is trying to process what we are saying to him. He definitely has a slower processing speed then a normal 5 year old. He is good follow two step directions but anything more then that and he is lost. Sometimes two steps throw him off.
Is your daughter doing speech therapy?
Jessie mommy to Gabe(5 years ASD/CAS/SID)and baby Zane (1 year old)
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She is using immediate echoing, and that is a great indicator that she is communicating. If she echos you when you ask her a question like "Do you want to go on the swing" what she is really meaning is "I want to go on the swing". You can then just interpret what she is saying and model the correct speech for her. So, if she says "Do you want to go on the swing?" you can interpret it and say to her "I want to go on the swing" and then put her on the swing.
A great book and video for this is More than Words. It gives parents and caregivers tools to work with kids that are speech delayed that are non-verbal or are early in speech. I have really seen my son blossom with this program. At 3, he was still using only 2-3 word phrases and now at 4, he is using full sentences.
She may be echoing for processing purposes.