It is not uncommon to occasionally have one "off" bird that dies. (If it happens too often, like more than one bird a year, you will need to investigate.)
It sounds like she was unthrifty, and that can simply happen. If she was very low on the pecking order, she may not have been getting enough food to eat which would have ran her down, which would have invited parasites, which would have produced the anemia, frailty, and death.
Keep your eyes open for any symptoms like bubbling eyes, wheezing, coughing, or other signs of ill health in the flock. Likely you won't see anything.
Check your flock for scaly leg mite (uplifted scales on legs), lice (straw colored slow moving critters around the vent with rice looking nits stuck to base of feather shafts), and mites (fast moving pepper looking specks). Check at the vent as that is the most common location for lice and mites.
If you see more scaly leg mite, you can coat every bird leg with vaseline. Retreat every few days. Keep that up until the legs look clean.
If you suspicion lice or mites, dust each bird at vent and under wings with permethrin type dust (usually called Poultry Dust). You can also get liquid spray permethrin (Gordon's for example) to spray the coop. Lice and mites live on the bird, so usually a good clean out of bedding with dusting of permethrin in the coop and on the birds does the trick. Retreat in 10 days.
If you see red pepper looking specks moving quickly on the bird at night, with clumps of pepper on the roost post or in crevices, that is Red Roost Mite, and your whole coop will have to be thoroughly cleaned and deeply sprayed with chemicals. Gordon's can help, but often you need stronger chemicals as RRM are very hard to get rid of. Most of us have the Northern Fowl Mite (grey specks seen during the day), that are much easier to treat as they do not live long off the bird.
If your birds look and feel thin and haven't been wormed, you can spend the big bucks for the poultry formula Aquasol, which is fenbendazole, or purchase fenbendazole as goat liquid wormer Safeguard. You can also get a Safeguard horse paste (pea size given in beak). It's the same drug, which is FDA approved for poultry, but only the "Aquasol" is actually poultry approved. It will be personal discretion how you feel about using "off label" products, especially the same drug. If I remember right, one treatment is enough (but check BYC forum).
Or, if you have a mind, and don't sell eggs, especially labeled organic, to the general public, you may consider treating with the Ivermectin which will treat scaly leg mite, mites, and the most common poultry worm type effectively (round worm) unless you've used it a lot and they have built resistance.
It is getting harder and harder to find meds for poultry at the feed store since the FDA's changed policies in 2017 determined to remove most meds from agriculture. It's unfortunate as animals need care, vets are expensive, and most vets don't treat common poultry. The big farms simply turn over flocks every 2 years or cull. They also have the room for proper field rotation to keep parasites down.
My thoughts.
LofMc