This was my family's situation I'll be as honest as possible. Sorry if I come over as too frank but good intentions do not justify bad actions.
It's definitely not about your need to see her - she now has a very limited amount of time and must use it how she wants to. And by all means bring flowers if you're invited round but don't send a 'sorry you're dying, have some tulips' gift.
People don't always know what they need until they need it. So the most important gift you can give right now is deep and intentional ACTIVE LISTENING.
My mum wanted to be treated normally and not talk about it. So the friends we most appreciated were those who respected that, and limited their visits to 40mins without being asked so as not to overtire her.
What we wanted most was for people to say that they would be there if we needed them and then, when we did ask for help, say yes - whether that was a lift to hospital, going for a walk with my dad, or picking up medication.
End of life stage has a more complex set of needs (and requires even more active listening so as not to impose on people's last days with their families) but your friend is not there yet.
The best people were the ones who listened, said yes and did what we asked without making it all about themselves. We had a meal rota at times (this site and the friend who co-ordinated it was a godsend: https://takethemameal.com/) and the ones we most appreciated were those who dropped it off at the door with a bottle of wine and didn't invite themselves in for a chat 'to see how we were'. Or the friend who came and installed a ring doorbell as we are all awful at DIY. Those are the ones I most remember and I will never forget their quiet kindness.
If you have a relationship with her son, you could just say how sorry you were to hear the news, ask if there is anything he thinks she or the family need right now and tell them to add you to a list of people to call on if they need ...[whatever you are able to commit to]. If you can't commit then don't make the offer as it's humiliating and exhausting to call someone who's said 'I'll do whatever you need' only to find that weekdays are difficult for them, they have pilates on Tuesday evenings and can't do Thursdays or Sundays. Give time constraints if you have any eg 'weekdays are difficult for me but if you ned any shopping dropping round in the evening or a meal I would be happy to help', or 'if your mum needs any lifts to and from hospital appointments I would be happy to help on Tuesdays'.
The next year will be awful for all concerned but I also remember it as a time when we were shown great kindness. That is the greatest gift you can give them.