First, OP, you have my sympathies.
I lost my mum a year past July to lymphoma. She went through 1course of chemo (1/2CHOP?), given all clear (well, depending on which doc you talked to) which came back about a year later. 2nd chemo hit her for six and it was palliative steroids only and wait for the inevitable.
She was amazing, never complained about how she felt, always said that every day was a bonus and she’d had a decent life. The end was quick, deterioration really accelerated the last week. I was lucky to be off work and able to nip in past pretty much every day for some extent over her last 10 days. She was very out of sorts the last day. She answered questions as if she didn’t understand them, non-commital, vague. Except at one point she looked right at me and asked, ‘this is Friday, isn’t it?’. It was. I went home in a state of some distress, I hated to see her so not herself. And feared she was losing her sense of herself.
She collapsed during the night or early morning. She didn’t make it to the hospital (my dad, bless him, stopped them de fibbing as she had a DNR).
I was relieved for her (her pain and suffering had stopped, she had been spared being lashed up to machines to keep her going, she’d have hated that) and, obviously distressed myself. My dad was poorly (he died 12days later) so I was the responsible adult and took over all the arrangements. I found solace in being the one to shoulder the burden and it helped me cope. My real distress was only alleviated when I caught up with the Loon, comfort in closeness.
So, do what you can, be as forgiving of what comes and giving of yourself as you can (I reproached myself for not having done enough,but in reality I could never have managed to do ‘enough’). Be there for her. Give of your heart.
There is definitely a void still. And I miss her. It has lessened though, over the while.
As long as by your actions your mum knows you love her, there isn’t really anything more.
Best wishes.