AITAH for refusing to give my sister the money I saved for my dog’s surgery?

I (29F) have a 6-year-old golden retriever named Milo. I got him when I was in a really dark place in my early 20s, and honestly, he’s the reason I got through it. He’s not just a pet to me — he’s family.

About two months ago, Milo tore his ACL (or the dog version of it) at the park. The vet said he needs surgery, and it’s going to cost around $4,800. I don’t make a ton of money (I work admin at a small office), so I’ve been picking up overtime and cutting back on everything to save up. I’ve managed to put aside about $3,900 so far. The surgery is scheduled for next month.

Here’s where the issue starts.

My older sister (34F) has two kids (8 and 5). She and her husband aren’t great with money. They just got back from a trip to Las Vegas in December, and they’re constantly upgrading phones, eating out, etc. Last week, she called me crying because their car needs a new transmission and it’s going to cost around $4,000. Apparently they don’t have savings.

She asked if I could “loan” her the money.

I told her I couldn’t because that’s the money for Milo’s surgery. She got really quiet and then said, “You’re choosing a dog over your niece and nephew?”

That stung. A lot.

I said it’s not about choosing the dog over the kids. It’s about the fact that I’ve been working nonstop to save for a medical procedure that Milo needs. It’s not cosmetic. He’s limping constantly and in pain. The surgery isn’t optional if I want him to have a good quality of life.

She said kids need their parents to have a working car more than a dog needs surgery, and that I’m being selfish. She also said that because I don’t have kids, I “don’t understand real responsibility.”

My mom called me later and basically echoed the same thing. She said I could postpone the surgery a few months and help my sister now, and “figure it out later.”

But postponing could make Milo’s injury worse. And if I’m being honest, I don’t trust that I’d actually get the money back anytime soon. My sister has borrowed smaller amounts before and it always takes forever to get repaid, if at all.

Now my sister isn’t really talking to me, and my mom is acting disappointed. Part of me feels guilty because I do love my niece and nephew and I know this situation affects them. But another part of me feels like I shouldn’t have to sacrifice something I’ve worked this hard for because they didn’t plan ahead.