Well that went as smoothly as I could have possibly hoped. The seller agreed to a refund, so I sent the pony back via USPS. The seller was unable to do a shipping label, I'm not sure if it was because the sale was international, or because her eBay shop was set to not accept returns. So I had to trust her on that part of it.
The refund came through yesterday, and she also sent me my return shipping costs through paypal. So she's as nice as she could possibly be, and seems to be trustworthy, but I just want everyone to be aware of the smoking issue if you are thinking of buying anything from her.
So thanks everyone that replied here for your awesome advice, and for calming me down when I completely panicked after first opening the package.