Speech concerns

My LO is just about 18 and only really has 3 words (ball, dada, and mama). She has 2 older siblings. She won’t even attempt to imitate sounds. My middle child gets speech services so I’ve been using the same strategies with her and nothing. She is getting evaluated in a month for services as well. I’m just curious is anyone else has been in a similar situation and what the outcome was. I looked up early signs of autism and the delayed speech is really the only one she has (but I know it’s not off the table yet). Thanks!