I used Melatonin for my Husband and it did seem to help quite a bit. I discontinued it when he began wanting the light left on when he went to bed. ( I was told that light counter effects the melatonin.) You need to check to make sure that the melatonin will not interact with any medications your Mom is on. It might take a while for it to work.
You also might want to try Lavender either a spray or a sachet under the pillow or by the pillow. A lavendar lotion might also work, rub some on her hands and arms before she goes to sleep, just a bit of a massage might be the relaxing thing she needs. sometims a "noise machine" that has the ocean, summer night, rain sounds might also relax her as well as cover other noises that she may hear while she is trying to sleep.
If all this does not work there is nothing wrong with trying medication to help her get a good night sleep.