I highly recommend Team Estrogen. forums.teamestrogen.com.
And like everyone else said, let HER set the pace. Ask her if she wants advice or not, and if she says no, don't give her any, even if she insists upon having her seat four inches too low and her cadence at 50 rpm. She might smack you later when she realizes you didn't tell her, but at least you won't be out on the side of the road with her threatening divorce. (This is the voice of experience - my husband is the less bicyclely inclined of the two of us, and my well meaning advice isn't always taken so well.)
When hubby and I ride together, I let him go in front so he's automatically setting the pace. We stick to low-traffic MUPs and roads with wide bike lanes.