Hi J.~
My son turned 3 in January, and although he was somewhat of a late-talker, now he is very verbal and does hold conversations well. But there is certainly a range for normal development of speech and language skills, and certainly not all children develop the same way or at the same pace, thus the range.
That said, however, if your pediatrician is suggesting that her lack of 'conversation' skills may be an issue, I would follow your peds advice and get her evaluated by a speech therapist. There is something called echolalia, which is a speech pattern in which the child essentially echoes what they hear others saying, or hears from tv, etc. Echolalia 'can' be associated with other disorders, so you may just want to err on the side of being overly cautious and have her evaluated... in the event that there is actually something more going on with your daughter, then early intervention gives your daughter the best opportunity for success. If you would like to chat more about this, you can send me a message directly here... I check regularly...
Keep in mind, though, that it may turn out to be nothing. I have a cousin who was nearly 4 before she started talking. They did the whole battery of tests, hearing, speech, developmental, etc., and found nothing. She is now a sophomore in college, a cheerleader, bright, social, and perfectly normal.
Best wishes to you...