C.A.
If you could take some time to visit, that would be the best. If you lived closer i would suggest helping out w/ the kids.
do not send flowers. cancer treatment and flowers do not go together.
you could send her a package w/ some comfy clothes, like sweats that are a little bit more fancy than grey ones.
she will need lots of lotion while she goes through treatment, get it un scented.
head scarfs. is she a bandana girl or a silk scarf girl? or baseball hats?
you might want to wait in the head stuff until she is actually losing hair-before hand she may just get more depressed.
having home delived groceries would salso be good.
since you are far away you could see about being the one to arrange help/dinners/gift cards/childcare/housekeeping via email. If you had access to her email-or her child's school, people could contact you, and you could then set up a calender. That would take a huge load off you.
the very worse thing is when some one asks, what do you need. Please don't ask, offer specifics. she has enough in her brain. I had someone fill my soap dispensers. Seriously, it needed to be done, they looked at me like I was nuts, but, they asked, and that was all i could think of.