I really feel for you and your situation. I once read something about how the funerals and mourning are for ourselves and not for the dead at all since they are at peace. I'm in a similar spot right now my Grandma helped raise my because my dad wasn't around, she has lewey body disease (like a combination of parkinsons and dementia) she's still alive but I've been mourning her for at least six months because she isn't who she used to be, she is angry and mean and it's so hard to have these last memories of her, meanwhile with all the stress going on with that my Mom had been losing weight but we chalked it up to stress..she actually ended up having a very rare form of Lukemia called CML where she has to take medication everyday for the rest of her life but should have a normal life span, but before it kicked in seeing her so weak when she's such a tomboy and handy around the house really broke me down. It's ridiculous how much cancer treatment is and how outdated a lot of it is. Luckily the drug she needs came out in 2010 without it the survival rate was less than a year... and just like your mom you wouldn't know it she barely told anyone and she didn't tell me until she knew exactly what kind because she didn't want to worry me.
We absolutely need to open up more and show people our real feelings while they are here because a funeral, flowers on a tombstone, it's too late, it might make us feel better but it doesn't fulfill that bond that we need with those we love.
Thank you for the reminder though again because any of us could die at any time, even just crossing the street or driving to work. I've been working on forgiveness and trying to be in the present more because of things like this, we only have the present to tell people we love them.