Please just don't say or do NOTHING! I have noticed that when people are struggling, it seems a lot of times that's when people retreat instead of stepping up.
Just text and say you are there if she (or anyone in the family) needs anything. Maybe start a food train and if you are close by, bring over a meal once or twice a week. Even if she isn't able to eat or cook, her family would still like a home cooked meal.
Be honest and say, I know you may not feel up to a visit or phone call, but I'm going to just randomly text you when I think of you. I know you can't always respond but you are important to me and I want you to know I have not forgotten about you. Then text her what's going on in your life and things she can comment back on if she wants to.
I would be in contact with the husband too about meals and cleaning and things she normally would be doing. The husband and kids (if any) are going through a lot too. Maybe offer to take the kids somewhere fun to give the husband a break.
I got very sick about 2 years ago and was in bed for a few weeks. It was helpful to get a few meals dropped off and for someone to pick up the kids and take them to the movies or public pool, etc. My husband puts in a lot of hours so those things really helped him. There's only so many nights you can eat fast food and/or canned raviolis before you're really sick of it.
You are a good friend for trying to reach out. Good luck.