Advice for how to approach parents about cognitive issues when they will be in complete denial?

The signs are there, but every time we've suggested that there may be some cognitive issues with our Mom, there is complete denial and excuses. I know this community has so much experience, and I'd love to learn from you. I have to be honest; her kids (me and my sibling) relationships with her haven't been great (for decades) ... we're trying to do right by her because she's our mom, but it's hard.

Things we've experienced so far ... there are the classic memory problems... showing up to places on the wrong days, asking us to take her to doctor's appointments on the wrong days, but she is exhibiting some other "lesser-known signs"... making TERRIBLE financial decisions, sleep problems (likely also related to her working night shift for years); she's also been diagnosed with "explosive personality disorder" (although, TBH, I don't think that is anything new). Her eating habits are awful; she has Chron's, so that can be challenging, but she focuses on carbs, and I know that can also be a sign).

I don't know what I'm asking, really; I guess mostly, how do you approach parents who will be completely in denial? Bonus: she was just diagnosed with cancer and can't afford to live where she is.