Child With Imaginary Friend & Dyspraxia

My child is 16 years old with an intellectual impairment. She has characteristics of ASD but hasn't been tested. She has speech and language difficulties (probably mild dyspraxia but not diagnosed). At the moment she can only recognise around 40 sight words.

She has always had an imaginary friend who she talks to at home but not in the public. She role plays at home, so she may ask the imaginary friend questions, and then she will become the imaginary friend who will answer back to her. I've never been too worried about this as everyone has told me it is quite normal for children with imaginary friends and especially ASD children. What I can't work out is that when she speaks back as the imaginary friend, her speech is perfect! Is this ok?

She seems to be enjoying her life, she is in a special needs school and is quite comforatable at school with her group of friends. I know she does get a little anxious/frustrated when I take her out of her comfort zones into the public, but so do most children with and intellectual impairment.

So should I be worried and take her to see a professional? Who should I take her to see? She is quite aware that she has a learning diability, so she will know if I take her to see a professsional and I'm worried she will get anxious about it.

Is there information I can seek out from the internet first? What should I be searching for?