I've read all the answers you have been given and would like to add my own 2 cents. First, you didn't say you were setting them up on a date; you said your stepdad is looking for companionship, a friend. Trust me, she is too. They already have something in common - the death of a spouse. Hers is more recent, however (again) your not setting them up on a date.
When my mother-in-law passed away, my FIL relied heavily on us. Then he moved back to Missouri and although he was close to his brother, he was lonely. He wanted companionship - someone he could RELATE to. He finally found someone to share a friendship with. My grandfather, same thing. After grandma passed, he needed that companionship.
I would stress to her that you are not looking to play matchmaker, she is just the only person you know close in age with your stepdad and they have something in common, including both being Christians. Remember, God does things His way and maybe you are his catalyst for bringing two souls together that need someone to relate to them. Don't feel like you are playing matchmaker, because you are not. There is nothing wrong with introducing your dad to a friend.
I do agree about calling her. Maybe you could meet her for coffee or lunch or something and discuss it with her. You might be very surprised at her reaction. People need to realize that just because a spouse passes does not mean the surviving spouse has to mourn for a specified period of time. They will always mourn their loss, yet it is up to them when they decide to continue living their life. =) God bless you and I'll pray for you and your dad and your decision.