I just got a new dalmation molly (and two red platies) to keep my female betta company. The molly has been staying at the bottom of the tank while all the others get along just fine. It was not the one I had picked out, as I later discovered when I got home and this Molly had been kind of...strange at the pet store as well. Should I give it a few days more to adjust before I start to worry?
Most fish will be acting strange after they get home from the store. My three platies didn't eat for a few days and wouldn't leave a certain corner of the tank, sticking close to the gravel. My betta also didn't eat for a while after comming home. Give her a couple days maybe 3 or 4 days. She should be fine by then, if not, then take her back. Best of luck!