Introduced my 2 cats (sisters) into a new house & one is now growling at

[j k]

her sister...should I be worried? I have two almost 2yr old stray cats that I rescued as kittens. They are very close (share food & litter, sleep together, wrestle, and clean each other) and have been together since birth. We introduced them into my bf's house after his cat had recently died and I moved out of my apartment and in with him. They've been in one room of the new house for 12 hours and the one is purring with me but hissing at her sister. The other is purring and fine. I'm not sure if she just needs to adjust or if I should be worried. His cat was a male that used to pee in random places. While they were used to me smelling like him, I think her smelling his marked territory is making her think it's her sister or that there's another cat. (They lived with their mom and another cat and dog as kittens before I adopted them) I don't know if I should be worried or if she will adjust and realize that it's just her sister. Suggestions?

 

[Chelsea FC]

It will just take time for her to adjust. Going into a new home is stressful, and she'll be hissy until she feels comfortable again.
She knows it's her sister, she's just upset and doesn't want her near right now.