Oh, these decisions are the worst and I am sorry you have to make it so soon. Ten years old is so young for a kitty
I have administered chemotherapy to kitties many times over the years and it can be a rough (and expensive, unless you have insurance) road for everyone involved. I would encourage you to see an oncologist, if you haven't already, to discuss the prognosis and treatment program for lymphoma--and what you can expect over the course of treatment. Some chemo is given IV and some can be given orally, check into the details.
My cat was diagnosed with a gnarly form of bladder cancer last year which forced me to make some decisions about what I was willing to do to treat her/it. Surgery to remove the mass, no problem--but my girl is a little firecracker and needs to be sedated for EVERYTHING so I knew IV chemo would not be an option. She would HATE it and it is a recurring event, the stress would be horrible for both of us. So, I opted for surgery and the less aggressive treatment with oral medication, no chemo.
In your case, there is no option for surgical removal and I cannot recall the protocol for lymphoma treatment These things have changed greatly since I was involved in treating cancer kitties. Should you want to consult with an oncologist, I can give you the info for who we refer to--she was the one I saw for Sophia as well. She is not exactly warm and fuzzy but she will give you the straight dope on what you would need to do/expect and what the prognosis is for kitties with lymphoma.
Best to you and your kitty.