I would go to the vet to rule out a bladder infection or some other kind of infection. Even if you do think its behavioral always good to rule that out.
And like has been said before make sure your litter boxes are always clean. There is a product called Feliway that is supposed to be calming (gives off calming pheromones) which might help if she's upset about loosing the kittens but at 8weeks old the mothers shouldn't be that upset because that is the age kittens become independent anyway. Good luck!