Had my two kittens lilly and rose from the same mother at six weeks old ,they both got different personalty's but have got on rely well ,but rose has just had kittens and lilly keeps being nasty to her ,rose is so sweet and has never been nasty and is wondering what she has done wrong.. I love them both what do I do to make things like they were ?

Is Lilly fixed? How old are the kittens? How old are are Lilly and Rose? How is she being nasty to Rose? Are they indoor or outdoor cats?

More information will help us give better answers.

It's not unusual for an animal's behavior to change when another member of their pack/family has babies. The dynamic within a community changes with the addition of other animals, even ones born into the community.

If the way you treat them has changes, it could be jealousy. If you're giving Rose more attention, better food, or are treating her different in any way, then try to even things out a bit more.

It could also be a matter of changing status. With cats, a female giving birth automatically makes her the alpha female (the female in charge, so to speak). It's possible that Lilly doesn't like that Rose took her spot, and is trying to get it back.