It doesn't sound as if she has settled well into preschool at all.
If she's never been with anyone but you and her dad up to now then it will have been a big shock to her system to have to interact with other adults who are in charge. I assume that when she's played with her little friends you have been there with her?
I would second Manamala's suggestion that going full time would result in better settling and more security. Four half days would have a predictable pattern - up, breakfast, school, home, lunch, quiet time, out again to play, dinner, bath, bed. Then three days (Fri, Sat, Sun) to decompress, then back to the grindstone on Monday...
She would have a chance to develop a connection with the staff and they would get to know her better and be better placed to make meaningful observations about how she's doing. The comments they have offered to you so far have been pretty generic, tbh.
I would seriously consider paying a teenager to come in and do Mother's Helper maybe two afternoons a week in your home while you get on with chores or take a bath or read or simply have a nap. After you get to know a helper better, and DD gets to know her, you and DH could maybe go out somewhere on a Saturday morning for a few hours. It's good for children to get used to other people's ways. It would also signal to DD that you are not her playmate, you're her mother, you take care of stuff around the house, you and daddy have a relationship that is separate from your relationship with her.