I can understand both sides I think.
On the one hand, when you have a cold, you wake up early really dehydrated with all your sinuses blocked and your head pounding. The thought of getting in a shower then out in the cold and being normal makes you want to cry. Last Monday I was the same, I slept a few hours and felt better mid morning, but still not enough to face the world. If you call in sick for that day you are entitled to be sick and not be expected to do any work. If my staff do this, that's it, I don't expect anything of them until they return to work.
By midmorning you normally transfer to the couch, watch shit telly, play on ipad etc. Most people feel very guilty about calling in, so they always make it sound worse than it is, hence the migraine. Who hasn't called in and even faked their voice into a weak version. I did this when I broke my arm! I don't even know why!
But it is hard picking up the pieces when people are sick, and I would expect soeone to be a little more discreet on FB. Posting that you feel lousy for sympathy is one thing, uploading and organising your photos hmmm I don't know.
I think I would bank it for now, just bear in mind if sickness becomes too much from one individual. If you do feel compelled to let her know you know IYSWIM, then ask how her migraine was and mention that a recommended way for a speedy recovery from migraines is to stay away from computer/ipad/tiny phone screens and rest the eyes.