Good ADC's with Annie?

Hello. My friend is trying to get better as support, and found to be fun enough for him to enjoy the role. Right now I have a limited champion pool (only marksmen I own are and ) and I have enough to get another ADC. I'm not entirely sure if I want another ADC to match Annie's weaknesses, or to boost her strengths, so any suggestion is fine. I had my eyes set on but I've been a Annie support with her and it didn't work out so well.

Anything is fine, even Vayne, I'd just like to know why it works well with Annie.