Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you with your wee one today.
Situations like this will always be difficult with our pets, especially as we cannot ask Jess what she would choose. In regards ***** ***** best treatment option, often we will amputate and then follow up with chemotherapy. That said, unless a cat is very docile and amenable to being poked and prodded, we do find that most are not keen on chemo treatment. Therefore, if she is a cat that does not want to be messed about, chemo may not be an ideal choice for her.
Now in regards ***** ***** question, as long as they xrayed her to ensure the tumor has not already spread to her lungs (the most common site for cancer spread), then the amputation is a reasonable treatment option. While you and I would certainly struggle with the loss of a limb (50% of our means of walking), cats tend to cope really well despite the loss of a leg. This is because unlike us, they are only losing 25% of their walking limbs and many cats recover from amputations as if that lost leg was just a spare (we even see these cats jump fences and go about daily cat life without issue). Furthermore, many cats feel much better after amputation because the surgery removes not just the tumor itself but all the pain it has been causing. So, at her age (which isn't particularly old), as long as Jess has good mobility in her other legs this would be worth discussing and considering for her.
Otherwise, if your family just doesn't want to take any invasive treatment steps (which is fair when most aggressive bone tumors only carry ~9-18 months survival time even with amputation depending on what type of tumor it is), then palliation with pain relief is an acceptable option as well. And if you were to find at any stage the pain relief didn't keep her comfortable enough for her to live a normal life, then that would be a cue to euthanize.
Overall, these are all viable options for Jess. In regards ***** ***** question, cats tend to do very well with limb amputations as long as they don't have any issues with their other legs. And this can allow them to continue to have a good quality of life even without that leg. So, if she is otherwise mobile, her chest xray (pre-op) is clean, then amputation would be worthwhile to consider to get this cancer away before it can spread, to stop it causing her pain, and give her some more time with your family.
Please take care,