We went to the King County Elections website together, and were able to confirm that she was still a validly registered voter and eligible to vote. With her consent, I printed out a replacement ballot for her. Then I handed it to her and told her to go vote for whomever the hell she wanted, but to please go drop her ballot in the ballot box across the street from the courthouse (two blocks from our office). And gave her time off to do it.
Someone voted today, because of me, who would not otherwise have had a voice. I feel good about that, and I really don't care who she voted for.