Should I put down my pet that's suffering from pain but is still enjoyng life

Just as the title said. I have a rabbit that has been suffering from chronic pain for months now. The pinkillers aren't effective. But her quality of life is...ok. She can eat, poop, move around. She likes being petted and eating treats. It looks to me like she doesn't want to die and is still willing to live. I don't know what to do. The vets don't know why she's in pain. She needs 2 more surgeries (she's an elderly bunny and she already underwent 3 surgeries in the span of 1 year) and chemo... She's on painkillers everyday but they aren't effective. I don't know what to do. Should I put her down now? Or should I fight for her more? There is a big chance the second surgery will get rid of her pain. Or she might die... I don't know and the vets don't care about her happiness. I'm from Russia. NOBODY cares about animals here, not even vets. What's the correect thing to do? It looks like she's not suffering to the point of being put down but it also looks like her life is hard.