I know I like it when people call to check on me, but sometimes I don't answer the phone or talk long because I'm not up to it. So, unless she asks otherwise (and it's okay to ask her if she minds if you call every day) go ahead, but don't be offended if she doesn't want to talk or talk long.
My mother, whom I love very much, often calls (not every day, but close) but sometimes I don't pick up the phone or, if I feel I'm overdue to connect, I'll talk but cut it short if I don't have the energy. Nothing against her, just what I can manage at the moment.
Take your cues from her. You can ask about her results, conversations with oncologist, etc. If she indicates she'd rather not talk about it, respect that. I personally don't want to be immersed in it, but I know the rest of my family wants to know where things are. Sometimes I'm more in the mood to talk. Generally I don't mind answering questions, but I don't want to dwell on it, but that's just me.
And, yes, talk about memories, family, let her do a "brain dump" if she wants and milk her for answers for questions you'd like to know about (if she's willing). I know one concern I have is that a lot of my experiences and things I know will die with me, and if someone would like to know how something was like or how I got through it, or what it was like at a certain time (e.g.: growing up with no TV, dirt roads, automats, WWII, whatever) I like to share. We are at risk for forgetting the past because it's generally not recorded. Not so much today, where everything is on video and twitter and the historical record is rich, but back when I was growing up and certainly when my mother was growing up, those times can get lost. She may not want to go back, that's up to her, but let her guide you.
The other thing is to try to make sure loose ends are tied up; she'll probably rest better knowing everything's in place so she won't be leaving a legal mess behind. I know that's a worry I have.
There are no prescribed answers, e.g.: call every 36 hours, no more or less. It's an individual thing and you should take your cues from her, but don't be afraid to broach a topic. You'd be surprised what people will talk about closer to the end that they wouldn't do earlier. I know I had subjects I never used to talk about, but now I realize there's no advantage for me to keep them hidden, and I'm willing to talk about things that previously I wouldn't.
Don't fret over what's "correct". Do what feels natural.
Best,
- Tab