I've already bought her gift cards and sent the information online.
It is a scam. 99.9999% a scam. If you were paid for buying these gift cards, for example with a cheque paid into your account, expect the money to disappear from your account quite quickly, and nobody will be willing to cover your losses.
If they told you why they want you to open a bank account, it would still be a scam, because their reasons would be lie.
Cut any contact, don't talk to them ever again, don't react to any threats (which will be quite likely to come), and don't give them anything. Ever.