my mom presented me with a question about her cats that i found strange and was wondering if anyone had any input... my sister moved back in with my mom and brought her cats. everything was fine but all of a sudden one of my sisters cats wont let my moms cat use the litter box! My moms cat had been having "accidents" and they couldn't figure out why until they saw my sisters cat hissing and chasing away the other cat. my sisters cat also wont let my moms cat go in the basement. Any advice?
The hardest years are those between 10 and 70. -- Helen Hayes
The suggested amount for litterboxes is one per cat plus one extra. Does she have just one? Even if she can't have that many, she could try at least one more. I'm not sure if having more will help if your sister's cat is aggressive like that, but it's worth a try.
Not only several litter boxes, but have them in different locations. Ideally, there should be a litter box on each floor of the house (1st floor, 2nd floor, basement-anywhere the cats have access) Also, be sure the litter pan isn't in a place where the cat can be "trapped" when using it.