Introducing a new cat to existing cat.

It's tricky with cats, sometimes it's just a case of giving them time and space to sort themselves out, but then I have had two cats for five years, and they hate each other! I got them together as kittens from a rescue and they got on fine then but have grown apart over the years! My SiL swears by shutting them in a cold kitchen overnight!

Unlikely they will be friendly to each other, hopefully they will just ignore the other one.Whichever is the more forceful and strong cat will decide terms.?

I would let them do it their way in their own time. Two years ago we brought a male kitten into the house and boy did our two female feral cats hate him. No fighting but the girls made their disgust known, didn't think they would ever take to him. Took a good few months but now they are all fine together. Good luck.

I've read, make sure they have separate places to eat, litter trays etc. so they can stay apart if they want to.

I agree with all the above, but also Feliway Friends Plug-in worked well with my cats - it dispenses pheromones that cats associate with the mother cat and their siblings, and keeps the situation calm.

Hope your cat has decided to come inside, as the weather is getting colder.

Give the newcomer a room to herself with litter box and make a great fuss of your own cat. He will at some point become so curious that he will be ready to meet your daughter's cat.