There is absolutely no evidence of this. It's not uncommon for someone of Gabby's age to have their own bank account.
Had the parents been on that account, they presumably would have discovered something was off much quicker than they did.
In the course of investigating Gabby's disappearance, subpoenas would be issued to obtain bank records, phone records, and other data sources.
The most likely scenario is that's what occurred here, and that's how the fraudulent transactions were discovered.
I'm sure there's video.