Yes it can, that's what I was on about with the whole "sealed" ballot thing but didn't feel like harping with the details. Once you fill out your ballot you encrypt it with your state election official's election specific public key and the attach it to the email—the digital "put it in the inner envelope." Poll worker confirms eligibility and puts just the encrypted ballot in the drop box. At this point in the process they couldn't look at the vote even if they wanted to. Then when it's time for counting they decrypt each one and count it.
Again is it practical or accessible to your grandma? No but it's exactly the same as mail in voting.