Hello Monte :)
I know all to well of headaches and migraines. I get them almost everyday and medication does not have an effect anymore for me. Like Ann said (above) have your daughter in law drink lots of fluids. Such as water, tea, milk, low sodium juices. Try to stay away from caffiene products like soda and coffee. That could just trigger the migraines. Speaking of triggers....you mentioned that she only seldom gets them, when she does she should think of what she was doing, thinking, and eating. Many times migraines have triggers and when you learn what they are, you can prevent them or make them less intense by avoiding such triggers.
Other things i do to help with my migraines besides drining tea, i like to just lean over the steam that comes up and breathe it in threw your nose. Chamomille tea is wonderful for that, or a peppermint tea fumes.
Lets say she has the migraine and there is nothing that is working like drinking fluids...she should take an ice pack and place it on her head, depending on where the migraine starts (front like the forehead, or in the back of the head) and hold the ice pack there for 15 min. This will ease the pain, but she must hold it there for that amount of time, or it won't hold to its full benefits.
And as far as light sensitivity, have her wear sunglasses even in the house. :) This may seem silly, but hey, if it works right?
If i think of anything else i'll let you know! Good luck :)