Marina, I'd be far more concerned about the possibility that the buyer will leave negative feedback if you don't replace the gloves with the size she really needs. I know it's not your fault as the measurements were in the listing, but an unhappy (and therefore angry) buyer is the last thing you need.

Anyway, as this ridiculously thought out "defect"system doesn't come into effect until August, there's no reason not to treat this buyer as you would have in the past, thereby guaranteeing a happy customer and positive feedback.