She could very possibly be in heat again!
Has she weaned the kittens yet? (And yes I once had a cat who got pregnant before the kittens were weaned!) But she may be trying to teach them how to hunt. Does she take the toy to them?
Does the toy have cat nip in it?? Sometimes that will drive a cat insane and they just act crazy for a bit and then go sleep it off. Kind of like giving kitty a good stiff alcoholic drink....
Will she let you pet her when she has the mouse? Maybe she just wants to play for a bit.
Good luck on figuring it out! Call your vet and they can give you some other signs of your kitty being in heat again :wink: