Are you doing your Aunts return? Or did the interest come in your name and ssn? I redeemed savings bonds for my deceased parents. Filled out the Treasury Form 5336 got it notarized and sent in with the bonds. 2 months later got the deposit. I got a regular 1099INT from the Dept of the Treasury with the interest in box 3.
Here's Treasury Info
https://www.treasurydirect.gov/savings-bonds/manage-bonds/death-of-owner/
