I understand your anxiety after loosing my Dad, Granda and other members of my family to cancer in the past 3yrs and now fighting it myself.

To be very honest with you, all you can do is provide as much emotional support as you can but remember you need support too. It's all to common for one or more individuals to try to carry the rest of the family but it's important to your Mam to remain healthy yourself by sharing the anxiety & stress. 
Please consider talking to your boss and if you have a local charity organisation that you can speak to someone completely impartial can be a help too.

Make as many memories as you can and lots of pictures also. Here if you want to talk x