This site offers free counseling for patients and families:
www.cancercare.org
1-800-813-4673
There is no RIGHT way to get through this. Just do the best you can, and you just have to trust that will be good enough. Take things one day at a time, and if you need to, one hour at a time. The only moment we have any influence over in life is the moment we are in right now. So make each moment the best you can. If you are overwhelmed, stop, step back, take some slow deep breaths, and refocus on whatever the task is at hand.
You need to make sure you are taking good care of yourself, also. A broken down caregiver is no good to anyone. Make it a point to include laughter as part of every day - even if at first it is forced laughter, that's still ok. Laughter is a non-discrimination therapy - it will bring about positive body chemical changes regardless of whether the laughter is real or not. Exercise your senses by reason of use: make yourself see humor in everyday life, and laugh out loud. Ask those around you to help.
Also, share the humor with your mom. Rather than seeming to make fun of her situation, shared humor is very important for her also, because it emphasizes the normalcy of everyday life (which can be very reassuring to someone who is very ill), and shows her that she is loved and still considered to be an important part of the family.
Make sure to talk to your mom, about anything and everything. Encourage everyone else to do the same. Keep her in the loop, unless she tells you otherwise.
At some point things may start looking very grim for your mom. This is an excellent preparatory article about end-stage cancer:
http://www.virtualtrials.com/btlinks/death.cfm
Sincerely,
Tre