Hi Joanna. Sorry to hear about your situation.
If the money is not your income, you should just file your return with your proper income, which at this point from you wrote is zero. It is on your sister to file taxes with her online business income. If the IRS comes to audit you, then you have some evidence that this income was not yours.
I hope this helps. Take Care.
Answered on Nov 16th, 2020 at 7:19 AM