Sick love bird, that died? any ideas, i dont want my other ones getting sick. (Symptoms listed below)?

she lost alot of feathers, down feathers. Over the weekend my housemate spotted her on the ground (they live in an aviary) sitting in the the rain. all the birds often spend time on the ground, stripping the grass for nesting material and picking up seed so i didn’t give it a second thought.

someone suggested she was egg bound, there is two nesting boxes in the aviary, one already has a bird and her 4eggs in it, the other box seems to be abandoned, as every time i add nesting material too it they pull it out and put it in the other one (so i gave up)

they were treated for worms about 2mths ago.

there was four love birds (3female, one male) and 2 cockatiels (both male) that live in the aviary, its about 3×1.5×2.5m. fairly big, and they have lived in it together since january, before that they all lived in cages (cockatiels in one, two love birds in two separate cages)

any ideas? i just dont want my other birds getting sick.
i’ve never seen them fight, ever, not even over the eggs or boxes

and in the last 24hrs she died, i check them in the mornings and i found her at the bottom of the cage this morning.