I'm sorry to hear the news. Because it has spread, she is not a candidate for more than making her last days enjoyable which you know.
Several things: if possible, I'd combine tramadol with another med besides an NSAID. If you must use rimadyl, watch her stomach very closely and have blood work done in 2 weeks the first time to check her platelets and kidneys.
Transfer factor is a good immune builder and may help.
Feed her what she enjoys and get her off the SD. I'd go to a no carb, lower fat like EVO reduced fat or CORE reduced fat because of her age. Or, any food not real high in fat she enjoys.
Sending prayers.