@Mellyb my sincerest condolences to you and a thank you for understanding the crappiness of MBC , I'm only 51 and have been fighting this for 2 years I guess the main issue is to continue to raise the issue in the community and to anyone that listens.
I'm very honest when people ask me how I'm going and my response is usually very confronting as you said at the start , this is treated as chronic disease but it's not , it's a roulette game that we play with the drugs , treatments and emotions.
Be comforted with the memories, you stayed strong for your mum and that gave her strength to keep fighting as long as she did, keep moving forward and talk about it to anyone who will listen and keep talking to your Mum she's inside of you ....
lots of love ....