I think you treat nursing slowdowns and nursing strikes the same way: you continue to offer, patiently, calmly, consistently- and you do your darndest not to feel hurt when your child turns you down. Believe me, I understand that the last part is tough!!! So many moms just feel utterly rejected and dejected when their baby expresses no interest, or even resistance, to nursing.
Why your baby would slow down... It's really hard to say. Some kids slow down or strike when sick or teething- in fact, if you haven't had her in to the doc, and had someone look in her ears, now is a good time to do so. Some kids just lose interest in nursing long before the average baby. And some kids go on strikes because of adverse events- for example, a friend of mine screamed when her baby bit her while nursing, and the baby went on a strike and never went back to the breast. Totally not my friend's fault, of course, because who wouldn't scream at an unexpected chomp in such a sensitive place!
I wish the were some sort of guidance we could offer in terms of how often it makes sense to offer, how much you need to pump in order to maintain supply... But these are such individual questions that I think all we can give you is rough suggestions. Offer before meals, offer after meals, offer in the tub, offer when she's relaxed and sleepy, offer when she's sad... You never know what moment is going to strike that's going to remind her that nursing is good for food and comfort. When it comes to pumping, I think that you want to maintain supply, but how many times you need to pump in order to do that is very individual. I personally would aim to pump at the 3-4 hour mark, if baby hasn't nursed. But maybe that's not the right strategy for you, since your baby prefers a fuller breast, and of you pumped right before she nursed you'd be pretty drained. So how about pumping right after she nurses, and maybe again at the 1-2 hour mark?
If your LO starts nursing again, then yes, your supply will rebound. That's ability is what has kept the human species going! If milk supply were easy to lose, I doubt we'd have made it out of the Pleistocene.