One, 5000 gold is a HUGE amount of money, and I mean HUGE. Probably more gold then most Athkatlan nobles will ever have in their lives.
Given how quickly you can amass such a sum, and the amounts of gold that go flying around in shops, temples and so on, it doesn't seem like such a huge amount.
Yes, but we're adventurers, exploring dungeons and discovering huge quantities of treasure. Also, the gold we leave at shops pays for magic. If you consider that a long sword, which is an very valuable weapon (if it's a good one) costs only a few gold pieces, I'd say that one gold piece would be enough to support a normal family for a month at least, probably several. Which is as it should be, since gold as a raw material is hugely expensive.
Two, the notion that one has to pay a whopping 25% interest over a period of SIX days is laughable. At that rate, nobody would ever loan anything from him.
He takes advantage of the needy. That's how he operates. However, six days is an arbitrary number, so if you've got any suggestions on a period of time that would be more balanced or logical...
One year would be an absolute minimum for such an interest rate. I'd say make it two or three, that'd make the whole scenario a bit more credible, since you'd have the Marlowe-effect: The woman buys considerable luxury for a long time, and will not have to worry about the possible concequences until much later.
Of course, even if she has three years to spend it, a sum of as little as 500 gold would provide her with a lot of luxury. I'd say take the last "0" off the numbers, and maybe dress the woman up as a noblewoman...