If she is good at circletime you could also go under the assumption that she has been held, read to , sang to etc and what she is totally lacking is play skills. She may be totally overwhelmed by toys and not know what to do with them. Have had this many times from kids who were with grandparents till they turned 18m-24m and then parents wanted them with other kids but the kids had no idea what to do with other kids. We had to start at step one and actually demonstrate how to use the toy of the day.
Thanks, playfelt! I have a similar situation as described, and that makes perfect sense now. I will spend more time on the floor with my LO and see if that makes a difference.