If your mother hasn't got a vet, I would suggest that she try to find one that specializes in cats and somebody that she feels comfortable with.
She could check with the pet food stores and friends for recommendations and work from there.
I have had problems with a couple of my cats from time to time with bloody stool and I was able to trace back to food.
But without a vet's diagnosis, it could become quite a guessing game as to what the problem is.
When your mother takes the cat into the vet, if she can get a fresh stool sample, the vet can check it for parasites and whatever else they would check it for.
Best of luck with this and hopefully kitty will feel better shortly.
Animals are such agreeable Friends.
They ask no Questions. They pass no Criticisms.