Luc,
I understand your frustration at not knowing - but remember, God is sovereign over all His creation, and the days are numbered for each one of us. Every human life is like a blade of grass or puff of wind, here then gone. It's not ours to know the when or the why, but when our faith is in a God who does everything:
"for the good of those who love him,[
j] who[
k] have been called according to his purpose. For those God foreknew he also predestined to be conformed to the likeness of his Son, that he might be the firstborn among many brothers. And those he predestined, he also called; those he called, he also justified; those he justified, he also glorified."
If this lady is a believer, she is soon to arrive in the kingdom of Christ where pain, illness and death can never touch her. At this moment, this may seem small comfort to her family, but she does have a blessing many of us don't: she knows the time of her death. She has time to say her good byes, make arrangements, start the process of closure for her family. Many people find this better than a sudden loss from an unexpected or random act.
We can pray for her to have peace in her passing, strength for her family, and that through her others might be blessed and find peace. I know I will be praying this!
Ryan