gran, I'm so sorry - I lost a dear best mate to ovarian cancer a few years back, and like your friend, she had no idea until it was too late.
Being there is the best thing - just being normal, still being her friend and doing things for her that she won't feel able to do - the odd magazine, a bit of shopping, buying her personal stuff (ladies' things) that she might not like others to do, or might not have the strength to think about.
We talked about holidays we'd been on, the good times we'd had - trying not to dwell on the obvious, but not denying it either, since it'll be at the forefront of her mind. Go out in the sunshine, listen to the birdsong which is lovely at the moment. Small things matter such a lot at this time.
Hugs and good thoughts to you and your friend ((♥))