Maybe you can try to (if you must, force yourself to) look
really concerned, look straight at her - and asks her what's the
matter, and does she want to talk? Then just listen...
hehe....
If you are close, you can hug her or just pat her shoulder will be
fine....
If she flares up don't take it personally, shes probably just PMSy
if she looks like she just wants to be alone, eg
turning away from you etc... maybe a simple, "take care, all
right?" will be fine in tis case i guess... 