Any ideas what happened to my cat?😭💔

TRIGGER WARNINGS GALORE

My 3ish year old cat (she was a stray that we found 2.5 years ago so this is based off the vets guess) died last weekend. We are so heartbroken and I'm riddled with guilt and confused. She has always seemed fine & healthy. No health conditions that we know of but again, she was a stray, so we don't know her history or anything. She seemed totally normal and then she threw up..didn't think that much of it..cats throw up. But it was bright yellow & foamy with some clear liquid. After she threw up, she just sat there..kinda still hunched like she was super focused on what just happened or like it was going to happen again. She just sat there...for a long time. That got our attention. It was like when she puked, she was immediately not herself. She would walk around and move places to lay..but slower than normal and would pick a spot and just lay there. I kept seeing her at the water bowl and in the litter box but never saw her actually drink or use the bathroom. Naturally, I called the vet the next morning (no one was open when this happened). My husband had mentioned that she had gotten into trash the night before puking and he had taken an old vienna sausage away from her. We (vet included) thought it made her sick. IMPORTANT SIDE NOTE: we were completely snowed in during this and could not leave the vet said to watch her close..make sure she was still using the bathroom (didn't tell me what to do if she wasn't), if she wasn't drinking on her own to give her some water in a syringe every couple of hours but that her belly was probably upset so not to force food. They said she could act sluggish and sickly for a week or so just from 1 incident of eating bad human food. So we continued to watch her and force feed water. 2 different days she perked up.. I saw her drink water on her own!! But then she started what I think was wheezing. It wasn't constant or even labored breathing from what I could tell. Just an occasional whistle sound on inhale. My poor baby was so lethargic and acting sick like this for 5 days with no way to get her seen 😭 then we found her behind the washer. My heart sank! Assuming she hid there to die. But we got her out and she was still alive!! But. Her mouth seemed almost glued shut. My only thought was ..is she possibly so dehydrated that her saliva is this thick?? I've never seen anything like it. It was like a thick, gray, jelly-type substance all around her mouth/gums. We got it cleaned up and immediately forced more water. It seemed to help. Everyday when we forced water, she was against it. She wouldn't fight hard or try to get away..but she'd try to clench her mouth shut. We thought she just felt so bad that she didn't want it. I've been that sick before... but this time she wasn't keeping her mouth shut as hard...we thought she was perking up and wanting it. But that night she rapidly declined. When I had finally thought we might be able to get her out and to an emergency vet that opened at 9am the next day (Sunday). It seemed like her back legs didn't work or were so weak that they couldn't. We spent hours in the floor with her..giving water in a syringe. Attempted some wet food mixed with water as well. But then she went from lying there with her legs kind of under her to her front legs sprawled out. And then she started yelling & thrashing around. Her front legs were like running in the air...and then she died. It was the most awful, traumatic thing I've ever witnessed. I don't understand what happened...other than it was probably not food poisoning via vienna. I feel so terrible that we didn't help her. Idk that we could've. But it's eating away at me that we didn't get to try. We did try...but we didn't have her seen. Which I know is realistically not our fault either because we couldn't safely leave. But. We loved her so much. Everyone in my household is autistic and has HUGE feelings and we are physically sick over this..struggling to eat & sleep. My kids are so distraught. They didn't witness her actually dying (thankfully) but it happened not long after finally getting my oldest to bed..he sat with her for hours as well, refusing to leave the room because he was afraid she would die not knowing he was there for her. We're just all so sad & the way our brains work....we want and NEED answers. And I know realistically we may never get them. But I can't help but try to piece it together and find a "probable answer" at the very least. I also have another cat that shared bowls and litter boxes with her and I'm terrified that it's going to happen to her too..since idk what is was. She won't make it 5 days of lethargy & not eating...she will be 13 in April. The snow is finally melting so she will be seen at the very first sign that something is off..but. Google has so many theories, but it's hard to search the timeline of things. And just the way she died...she seemed so scared. Or in so much pain. Or both. The look in her eyes...it was like she might have even been blind by then. I'm just so lost and heartbroken and confused...so any insight on what this sounds like it could be could help. Sorry this is so long....thanks if you made it this far🤍 I'm just having a really hard time with this.