Over a month ago, my family adopted a new cat. We already have a cat and our original cat has been around other cats, so we assumed she'd be okay with this new cat. We expected some hissing and huffiness, but it has gone wayyyy beyond that. The new cat tracks down and attacks our original cat. Like, runs right up to her and starts smacking the crap out of her. Now my original cat is freaked out and won't leave my bedroom. She holes herself in there almost all day, only leaving for like 15 min at night to sneak out to eat and use the litter box. This morning, New Cat decided to go into my bedroom and start whacking Original Cat. Original Cat freaked out and gave this deathly howl and jumped on my bed and peed. What can I do to help them at least tolerate each other? Original Cat has never peed outside her box, I know she did it because of stress/anger and it's not her fault, but I don't want it to happen again. I feel so bad for my OC because she's my baby and I don't want her so upset at New Cat. Every time New Cat even walks by my bedroom door, OC growls and hisses because she's afraid of New Cat. It's been over a month, shouldn't they be used to each other by now, even a tiny bit? I don't want to re-home New Cat because other than attacking OC, she is a great cat. How can I stop New Cat from attacking Original Cat? How can I help them get along?
Edit: Should I put a food dish in my room for Original Cat? I don't think she is eating enough because like I said, she holes herself up in my room all day. Should I put a litter box in there? Or should I not and encourage her to leave?