Update: There was a lot more going on internally than we thought (cancer, thickened intestinal wall, low heart rate,etc.). We couldn't watch her suffer, so we had her put to sleep. She was in my arms, curled into me because she was always super attached to me and I didn't want her to be scared.
I said St. Basil's and St. Francis' blessings while we were waiting, and offered a prayer for her (even though I know animals aren't fallen like we are). I know a lot of people don't think animals go to heaven or have souls, but I was taught otherwise. I just ask that you keep her in mind. It's honestly really hard to type this atm. My grief is pretty surreal, but I don't know where else to go. I know God has a greater plan, and I know I shouldn't get in the way of it, but still it's a bittersweet thing.