We have a tabby girl (Mia) who is 8.5 years old. We've had her from a kitten, and when she was approx 9 months old we got another kitten, a boy. She hated him for a few weeks but then they bonded, sadly he died 3 years ago.
Approx 5 months ago I got a new kitten, a 6 week old tortie girl called Rosie. I introduced them slowly but Mia immediately hated her.
Since we got Rosie, things have gone from bad to worse. Rosie adores Mia and wants to play with her. Mia hates Rosie and will hiss, swipe and growl at her whenever she sees her.
What makes me sad is that Mia (who was previously indoors 99% of the time) now stays in the garden to avoid Rosie, come rain or shine. She comes in for food and straight back out. It upsets my 5 year old whom adores her.
When the cats are in together (only ever if its because I've locked the cat flap), Mia will either stay in the kitchen by the back door (hissing, growling, swiping if Rosie enters) or hide in my daughter's room. She will no longer sit on the sofa, enter the living room or go anywhere else.
Today my daughter cuddled Mia, as she has done since birth, and Mia scratched her. Her temperament is like this because of Rosie. Mia no longer has the patience for cuddles which I can only assume is because she feels 'trapped' and vulnerable to Rosie whilst my daughter is cuddling her. This has broken my daughter's heart.
I have tried feliway, zykleene, rubbing washcloth on both cats, nothing works. If I stroke Rosie and then Mia, Mia will attack me, hiss etc.
I am expecting a baby next year and I really do not want this stress. With winter coming I am desperate for Mia to revert back to being indoors.
Hubby thinks we should rehome Rosie but it would break my heart as I would forever wonder if the new owners were nice, or if they hurt her or worse. None of my family or friends can have her

Is Mia changed forever? What can I do?