Etsy is not a flea market. You shouldn't have lowered the price in the first place.
If you happen to have a coupon code floating around at the time then great, give her the code, but you're running a business not a one-time 'everything must go' stall.
And anyways, as sellers we ALL reserve the right to refuse business to someone. I haven't yet but goodness knows if I felt suspicious about something then I would.
If she's not purchased yet then just take it off reservation and put it back to full price. If she wants it that badly she'll pay full price or take advantage of your sale if you're having one. It's possible that she's been after what you're selling for a very long time and just can't meet the price, but to ask you to lower the price, then hold it, then hold it longer and lower the price again is suggesting someone who doesn't really see the value in the product, or is looking for something on the cheap.
Personally I wouldn't blame you for refusing business at all. She won't like it, so I suggest that you firmly (not aggressively, just firmly) inform her that you will not lower the price further, and that if it isn't purchased within X amount of time, the reservation will be removed and the product put back up to full price. She'll either buy it then and there, or won't bother.
It comes down, really, to how you want to run your business. If you're in great need of cash then lowering the price for a single sale is more understandable, but if you're doing it JUST to please a customer then it's not really a good reason. Yes, we need to please our customers, but there is a line.