My ds with DCD and expressive language disorder had similar issues with conversational language, especially eye contact. He is slow to respond/answer at times (not always) and that's related to his DCD (DCD and ASD have overlapping traits in this and some other areas). Like your dd, he isn't shy and he can be actively and obviously engaged in some conversations at some times - but if you look closely you can see clues re when he's able to freely converse vs when conversations are going to be more halting and delayed etc.
What helped our ds was Speech Therapy that was directed at conversational skills and specifically worked on things like eye contact etc. In some ways his SLP approached it in a very scientific, almost mathematical way which resonated with ds. Having the instruction come from someone other than a parent who was always saying "look at me!" was helpful too.
Best wishes,
polarbear
