Tumor Opinion: Euthanasia or "making her comfortable"

My previous post discussed the possibility of Tulip being affected by her new bedding. After getting her to the vet last week, it was concluded that she had some calcium buildup in her bladder, though not stones. She was prescribed metacam to see if that might alleviate some pain and get her moving while the buildup passed with extra fluids and veg. I thought she was getting better, as they always seem to put on, but her weight begin declining again yesterday, accompanied by a new gagging/heaving symptom. I called for another appointment today, and after the vet re-examined the x-ray from last week's visit, she gave me the news that there's a mass in or around her liver. She says it's likely a tumor, though a needle test would need to be done to figure out if it was cancerous. In which case, surgery is $700 to remove the mass, and she expressed her doubt. She's only 2.5 years old, which gives the possibility of her developing more tumors, as spotting them at such a young age is likely due to genetics. She said the surgery itself, given the position, is also risky.

Anyway. I am trying to decide whether I should let her live out her days or put her to sleep. Getting past my emotions and tears is hard, and unfortunately I have to make this decision quickly. With the terrible timing of the world, I am also moving 40 minutes away tomorrow afternoon, which will undoubtedly be stressful for Tulip, while also distancing us from the vet. She's still making an effort to eat and move around, though minimally, but the heaving obviously impacts her. I want to be cognizant of her cage-mate, Opal, because I know it's advisable for them to recognize the other's death, so that makes me lean towards "making her comfortable". But I don't want to be unfair to Tulip and let her to continue to suffer. Any thoughts?

Here's a picture of my little love from a couple months ago, just because.