I agree with the not decarding option. It's a fallacy that major flaws on a pony that's MOC can be magically fixed by removing them from the packaging...often if they've developed flaws WITHIN the packaging, and yet the package is still sealed, that suggests it's something deeper going on and probably all you will do is reduce her value and take a rare item out of the market. Which is not good.
I have seen that pony on ebay before too, and I love the card, it's beautiful and very rare to see, but she was always out of my price range so I never followed it up. It's a shame she's so damaged but I would still keep her as she is.
If you don't like her, you can try to return her or sell her to someone else in the community...but honestly, given the rarity of one of that set in the original package, if it were me I would probably just keep her as she is...?