I am so sorry to hear of your mother's diagnosis. By now, you must have biopsy results, and a sense of how serious gallbladder cancer is. I was diagnosed almost 9 months ago, and was asymptomatic for most of the time, following surgery to remove my diseased gallbladder and do a bypass for my blocked bile duct. Some folks progress very quickly to the later stages of the disease.
I know of one man from another discussion board, who has cholangiocarcinoma, which could be GBC, or bile duct cancer, and he's at 8 years. I don't know of anyone who has lived longer. There are some active discussions on the site, cholangiocarcinoma.org, and if you haven't found the site, it's absolutely worth checking out.
I have a website about my journey with this disease that you can check out if you are interested. I try to provide information, links to other sources, and my story as I struggle with the disease. It's at www - dot - dahlborg - dot - blogspot - com. (I'm trying to keep this site from deleting the address, so you will have to translate.)
Good luck to you and your mother, and your whole family. This is not an easy disease to face, and I wish al of you the best.