ARGH please help new cat has attacked our gorgeous other cat.

[StrumpersPlunkett]

I was expecting her to be a little more tentative, reserved, she is v v friendly with humans but this was her first meeting with the resident cat.
resident cat went to investigate v slowly, not fluffy or over worried and new cat launched biting scratching I managed to get her off but she bit me and scratched all up my arm.
Poor resident cat did a wee and is now moving round the house very frightened, new cat is back in the dining room whilst we decide what to do.

HELP!!

Both girls, Strumpers ? And how old is each?

Did you separate them overnight?

Yep both girls. Resident cat is 3 yrs old and new cat is about 18 months
New cat has been here a week in the dining room with 3 visits of her being in the carry box whilst resident cat came for a sniff.
We talked overnight and dh is really feeling like throwing in the towel but I don't want to!

Ok, take it back to the beginning and introduce them properly. Jackson Galaxy here has a few YouTube clips on how to do this plus more on how to stop cats fighting. I recommend you watch them.

Did we get it very wrong then?

Just watched that. Thank you!!! Will go back to square one and do the feeding bowl thing to start with.

today we took her back to the rescue center. Glowing review on her personality with people and children but her aggression with resident cat has made us all too warey. Resident cat has been hiding in the kitchen and running out if the flap each time she has heard new cat talking. It didn't feel fair to her for us to keep on going.

Oh dear. I hope they updated her details to say she's to be an only cat.

They were lovely about it. We filled in loads of forms about her character. She was 5/5 for everything except for contact with resident cat. She will find a lovely home and make a lovely family pet.