She is the most beautiful tortie I have ever seen! Congratulations !
We are a multicat household, five to be exact, but I don't have any advice to offer you. We had been extremely lucky introduicing the new members, they get along from minute one!
Oh well, Little Pericot the newest one hissed a couple of times to the residents but after five minutes, no more, he was already playing with our flyffly Ginjol.
Koxka, the girl, compains about everything and everyone...so it doesn't count.
It seems things go quite good at your home too .George even let her share his bed and was relaxed enough to take a nap,! So I presume he is not very worried about Milly. So I would say let them go their way.