Unusual Queen death ?

Only had bees three seasons, but this was a new one for me. I've been having trouble keeping queen alive this year, between rolling some, having loose virgins kill purchased queens and not get mated, and so on. A purchased queen was placed in a very small hive after I lost a queen (rolled her I guess). She was slow to lay, only a palm sized patch of brood after release in a week, but I figured the population had dwindled to the point there were not enough bees to cover much brood. I added two frames of mostly capped brood and their covering bees to the hive to boost her numbers, hoping she'd pick up the pace. I saw her on a frame as I was inspecting, which I didn't pull out of the box (she was well marked, and I happened to see her after pulling other frames). When I went back to check on her a week or so later, I found her dead on the bottom board under a cupful cluster of workers, and seven new capped emergency cells on the donated frames. The number of bees on the frames I gave this colony was larger than that of the hive's remaining bees. I'm pretty sure I didn't roll her, but it's always possible. It seems the added bees decided she wasn't up to snuff and started to raise their own. I thought bees on brood were accepting of almost any queen. I didn't try to shake foragers or older bees off the frames, just pulled them and any clinging bees. Perhaps I should have tried to remover older bees from the donated brood frames?