I too won't plan too much up front or structure lessons - that might be too big a commitment. As a start, why not ask if you can be in her kitchen to watch when she is cooking? Suggest a specific day to get the ball rolling instead of one of those nebulous 'some day let's...'.

Then as lhamo suggests, bring a bottle of wine, and play it by ear. If you ask questions and she seems to enjoy answering, or if she volunteers information as she cooks, go from there. I certainly wouldn't suggest something long-term because either you or her might not like the dynamics of the situation. Do it once, and if it is fun for both of you, say 'Hey, this was fun, can we do it again? How about next Thursday? Would that be convenient for you?" If that one goes well too, then you might suggest something regular. Getting something like that started sounds like a really fun idea.