If I knew what I knew about alcoholism years ago, i probably would have run a mile back then.
My bigger concern relates to the fact that she is both unwilling and unable to look after herself. Drinking to deal with a cancer diagnosis is the ultimate in lack of self care. The drinking won't make the cancer go away, and the cancer hasn't stopped her from drinking.
Building on this - relationships are built on mutual trust and support. What happens if you need support down the track? If she can't look after herself, she can't look after you.
I've been thinking about things lately and realised that if I were sick in hospital and unable to fend for myself, who would I want overseeing my affairs and making decisions on my behalf? It certainly wouldn't be an active alcoholic. I'd want my sober, sensible best friend or someone I could rely on.
I see red flags ahead. Just my opinion though.
Wishing you much luck and strength.