My daughter is in 2nd grade and has yet to meet her preschool goal of reciprocal conversation for 3+ turns.
I know the frustration because we had that goal for years. Can your daughter reciprocate actions? mimic others? These are signs of social engagement and just as important as the speaking part. I think my son's inability to have conversations is due to his difficulty in accessing the words and structure of language to express. He demonstrates to me compassion and caring, so I'm encouraged by that.