Unfortunately LM is right.
This is one of those 'rumours' that still really frustrates me. It was invented back in a time when there was a mad craze to label everything that was a batch difference or a faded pony as an international or UK exclusive. It got included on DV and some disreputable UK people started making money on it, so it kind of stuck around for a bit. I think this one has refused to go away because sites like Strawberry Reef still claim it exists even now when it has long since been disproven.
In any case, I would say blue symbols prove fading rather than variation. A batch difference pony would maybe be paler but would still have properly purple symbols. And even if she was a batch difference, she'd still be worth the same as any other Windy, as it all really depends on the buyer.