While its entirely possible someone loosened the lug nuts, I would suggest inspecting the wheel for damaged lug nut seats or convex mounting surfaces on wheel or hub. Once they loosen a little bit it's possible for one or more to come off completely and behave exactly as you describe. It may just be that they weren't torqued the first time and now are suspect after being driven on.
Someone could have also stolen a couple and the other 3 were not enough to maintain torque. Seems unlikely if it's happened twice though.
Anyway, check it out just to be safe.
Idk I had the front end up in the air Sunday and checked everything for wear and the wheel was not loose and there were no nuts missing. I rotated the tires about 1500 miles ago and it was all tight. She went to work Wednesday and parked in the back lot and Thursday said her car was way worse. Im wondering if someone was trying to steel the wheel. She won't be parking in the back lot anymore. Last time a nut was missing was after Firestone put tires on but all the rest of the nuts were tight and I didn't notice it until I rotated the tires.