Just my speculation based on personal experience: I'm a joint account holder on each of my kids' checking and savings accounts. (My name doesn't appear on checks.) These accounts were started when my kids were minors so an adult had to be included.
Once my kids reached 18, their accounts were converted to regular ol' adult accounts. Each had the option of removing me from the account, but none did. It was easy for me to transfer money from my account into my 19 year old's account for school expenses, or transfer money from one kid's account to another to reimburse for a purchase (they use Venmo for this now, but for larger amounts they rather an account to account transfer, which I can easily do).
When I log into my bank app, I see the last four digits of all 11 accounts on which I'm a party.

As my kids change banks, marry, etc. I'm sure I'll be dropped from their accounts (as I should be).
I know Gabby's mom lives in NY, but I think her dad lives in FL. It's possible either of them are joint account holders on Gabby's account(s). Just my speculation -- keep in mind I may have missed new facts suggeting otherwise.