The title sounds REALLY bad but hear me out.

I have a 3 year old American Bulldog with a history of killing small animals. He’s very sweet with all people and small children, and plays nicely with larger dogs. But he has a high prey drive and will absolutely take off after small animals. He killed a total of three cats in his previous home; animal control didn’t put him down because every incident occurred when he was in his own yard (fenced in) and the cats entered. He isn’t considered to be an aggressive or dangerous dog. I understand this is probably upsetting to a lot of people, but it’s pretty common with dogs. They don’t understand the cat is someone’s beloved pet, they just see prey that they want to hunt down and eat.

I make a lot of money as a software engineer, and inherited a 4-bedroom house from a family member. I rent out one of the bedrooms to “Rachel” (26f), a friend from college. She pays me $300 a month, which is absurdly low for the area (San Francisco). Rachel doesn’t make much money and I really just enjoy living with a friend, but I am technically her landlord.

About a month ago, Rachel came to me and said our friend from college (really just Rachel’s friend; this girl was more of an acquaintance to me) “Ashley” had just broken up with her boyfriend and needed a place to stay until she was back on her feet. I told Ashley she could stay with me rent-free for two months while she looked for a new place and saved a bit of money. Ashley gladly accepted.

It came out soon after that Ashley had a cat that she wanted to bring with her. I said absolutely not, as my dog is aggressive with cats. Both Ashley and Rachel tried to convince me it would be fine, and Rachel kept saying she’d never seen him be aggressive with cats (but the reason for that was literally because I never let him around any cats...). They suggested my dog be confined upstairs and the cat get the downstairs, and I said no because it’s too risky, but also because I own this house, I was doing a favor for someone who really needed it, and my dog shouldn’t be punished because of that. Ashley said she had nowhere else for the cat to go and she might end up in an animal shelter, and I said since she wouldn’t be paying rent for 2 months, I was sure she could cobble together the money to board the cat. My last words on the matter were, “I don’t care where your cat goes, but she can’t come here. I’m sorry but if you’re not willing to find another place for your cat, then you aren’t welcome here.” Mind you that these conversations took place in a group text message, so there is evidence of me saying over and over again that she couldn’t bring her cat.

I thought we were all on the same page about this, but when Ashley showed up to move in (while I was out and Rachel was home), she brought the god damn cat. I don’t know if she was planning to hide her from me or what, but the cat didn’t even last until I got home. The two of them corralled my dog in the kitchen using chairs and let the cat out. The second he saw her, my dog went nuts, crashed through the chairs (he weighs 80 freaking pounds so I don’t know why they thought the chairs would keep him out), and mauled the cat to death.

When I got home, I lost my god damn mind. The two of them kept saying that my dog killed the cat, and I screamed that THEY killed the cat with their stupidity. Ashley threatened to call animal control, and I told her she should explain to them how she was instructed by the homeowner to not bring a cat, and she decided to do it anyway. There was some more screaming, and I eventually just told them both to get the fuck out of my house. Ashley hadn’t brought any of her stuff in yet and I told Rachel her stuff would be on my front lawn the next day (she didn’t technically have a lease with me but I know I would’ve had to formally evict her if she threw a stink; luckily she just agreed to leave).

Rachel and Ashley are splitting a one-bedroom apartment now, and I live alone. I’m honestly done with both of them, as I can’t believe they’d be so god damn disrespectful of me, and to put both of our pets in danger like that after being told not to. The issue is that Ashley says the cat was a British Shorthair, that it cost her $1500, and she wants me to pay her to get a new cat. I’ve been getting increasingly angry text messages from her, and she’s also told all of our friends that I have a killer dog (although most of them agree she’s in the wrong, once I show them the text exchange where I explicitly ban the cat from entering the house). She’s even messaged my parents about it, who already knew the situation as I called them about it hysterical after it happened.

She’s also threatened to sue me, but I think it’s bullshit. I think she must know she’s in the wrong, otherwise she would’ve gone through with calling animal control, or would’ve just sued me by now. I think she just thinks she can wear me down. What should I do? Should I just ignore it until it stops?

EDIT: I’m getting a dog trainer to try to help with the small animal aggression. I’ve only had him for 8 months and actually was looking for a trainer right before the pandemic hit, so it got put on the back burner. Thank you for the suggestions though; I do know it’s an undesirable behavior.

Tl;dr: Friend brought a cat into my house after being explicitly told multiple times that my dog is aggressive with small animals, and the cat wasn’t allowed in my house. Now she wants $1500 for a new cat.