Hospice Cat injured in my care

I feel terrible. But there wasn't anything we could've done truly.

My partner and I were wanting to foster to adopt a cat/kitten to be a mouser for our home. It's a long story as to why I picked this senior cat but basically a friend of mine brought her to the rescue and she had my favorite coloring on a cat and I wanted to give it a shot. (Color obv doesn't mean anything but I'll be honest, it caught my attention!) My friend had also mistakenly thought she was a younger cat due to her small size so I agreed to fostering before knowing she was much older.

We have mice in our basement so we would let her hang out down there whenever. She would sit by the door and we open the door for her to go down. We would leave her in our guest bedroom or basement when we were not home, whatever she wanted. She would climb into our open pantry (no doors but also nothing appealing for cats other than being a crawl space) in the kitchen and on our kitchen table and we just didn't want her doing that while we were away. It mostly bothers my partner so we were attempting to train her not to (she's old I know but we wanted to give a shot, ok? Lol)

Well, I got a call from my partner while I was at work that he came home to the cat not using her back left leg. No blood, no scrapes, no loss of hair or anything. I'm guessing she fell off a shelf in the basement. When I got home I looked in the basement for any signs of what could've happened and didn't have any success.

I keep beating myself over the head thinking "why did we let her in the basement?". But the accident could've happened anywhere in the house with how little muscle she has and how skinny she is. But I still can't help but feel responsible, the bedroom would be the safest place for her but we did want to see if she would catch any mice.

I offered to pay a portion or all of the vet bill if provided a receipt (I've heard of sketchy stories of the rescue handling cash in suspicious ways so I would think that a proof of the bill isn't a bad thing to ask for. Do correct me if I'm wrong) The worker at the desk did not seem happy to me offering that but maybe because I requested for the receipt I annoyed her idk.

I've fostered about a dozen kittens from a different rescue before this whole situation and have never had something happen like this but she was a special case with her medical needs.

The rescue actually didn't get back to us until almost 72 hours after the incident. My partner had called them before he even called me the night it happened and I left a message the following morning and the morning after that. They said the coordinator for the medical line had a day off. How could they not have backup for emergencies like this?

What would've happened if she had a bone sticking out?

Why does it also feel like I annoy the shelter workers by going in there. BEFORE I even picked her up it just felt like I was invading their space. I never felt that way with the other rescue at all.

I'm typing this all before going to sleep so sorry for any strange spelling or grammar.

Tldr; hospice senior cat mysteriously injured her leg in my care. I feel terrible.