Is this considered a scam?

I'll try to keep this short.

My aunt somehow convinced my grandma to go to the bank and open a credit line of $11K. She cosigned because my grandma makes barely anything ($300/mo). The aunt used it for a couple years and took her name off recently.

We just looked at the statements because we found out it was maxed with a $400/mo minimum payment. Grandma can only pay $300, mind you. The statements were all made on the aunt's card, with some obvious proof (based on amounts and shopping locations) that she was the purchaser.

I just found out about this unfortunately. The aunt has refused to pay a dime because she's not on the credit line anymore.

Is there anything that can be done? I'll appreciate any advice I can get.

Edit: New stuff I've learned. There may be other documents signed by papa, who does have dementia. We don't know what he signed, because he doesn't know what he signed, or won't tell us. This is now the bigger red flag IMO, I'm thinking life insurance or something else monetary. He gets very angry about everything, and hasn't told the family what he signed, but I really just want to see this through and make sure that rights are made right.

These are my spouse's grandparents, who are both elderly, and have worked all their life to make very little at the end, with their daughter taking full advantage and riding off into the sunset thinking all of this is okay. I don't want to see them go through this.

This is all occurring in the state of Washington. I have plans to contact the WA DSHS (Social and Health Services). If it goes to the authorities stage, it will be initiated by them.

Edit 2: Reading the comments, it's obvious now that "cosigned" is the wrong verbiage. The banks would not allow this. Which means that the aunt was just using the card, somehow "authorized", and that still doesn't sound right.

I'm working on convincing the affected parties to prepare for Monday. The aunt footing the bill has already given up her life goals due to how much is owed on this card that her mom can't pay. Shitty ass aunt dumped her mom to her other sister after she was done with her, and she is in grandpa's ear like Jafar or some shit. She was taking him to the city to sign papers, and nobody in the family was aware of what was signed. Nobody wants to step on toes, which is fucking silly to me.

I will use all my energy to ensure this gets right.