Have I made the wrong choice?

When I was younger I was very suicidal and frequently in and out of therapy, made several attemps on my life. My mother didn't know how to handle it. Someone suggested to give me a dog, it was a hell of a gamble but she did, which fortunately paid off. On new years day she gave me a ten week old puppy

For the last fifteen years I have loved and cared for this dog, her name is Suzie Q and we have been inseparable. My mental health has never been perfect but she really is my anchor that keeps me grounded. So you can imagine how I felt when the vets told me she has lymphoma. The news was heart breaking, then they asked what I wanted to do. I could try her on chemo, it could put the cancer into remission, buy her a year, maybe more of life. Or start her on pallitive care, which would still buy her some time but not as long.

They told me chemo would be very invasive, that even if successful at her age she could still fall to other conditions that would end her life. I wanted to squeeze as much time with her as possible but it felt selfish. To make her go through that just for my sake felt wrong. So I opted for prednisolone, a steroid treatment that would shrink the cancer, making her more comfortable as she lives out her life. They told me starting this would lessen the effects of chemo so there was no changing my mind.

It's been three days since I started her treatment, she still acts so happy, still has so much love and life in her eyes. I'm starting to seriously doubt my choice. Should I have put her on chemo, have I ruined her chances at it now? Have we passed the point of no return? These questions are flooding my mind and when I look at her and think of what I have done, how little time she has left, my heart breaks.

She's been my light for so long, kept me going through my darkest days, I can't bare the thought of losing her and I don't know what to do. Please, any advice you can offer would mean the world to me.