As mentioned, a chargeback will likely cause some complications. It definitely will lock the account and make it unplayable until the balance is settled.
Without looking at the account in question (I would need a character name/realm for that), I can only guess at what happened. It sounds like she may have linked to her WoW#1 license, though I’m not seeing a recent link on your WoW license, but either created or upgraded a different WoW license when she made the purchase.
I’d need to look at the account to get a proper timeline.
I don’t know what could be done at this point. Game Masters aren’t able to link accounts, it just isn’t an ability they have, but I might be able to see what happened.