During the dive I don't think that there is that much you can do. If you haven't already, invest in a good thick hood and some gloves, rental hoods and especially gloves have to put up with a lot of abuse and won't be nearly as effective as a personal set, especially a new set. The lobster style gloves are the warmest I've tried, but some people don't like having three fingers in one compartment, I know I don't. Depending on how well the wetsuit fits her, you may want to try putting some electrical tape around the wrists and ankles to restrict the flow of water. This shouldn't really be necessary for a properly fitting wetsuit, but it can help if the wrists and ankles are a little loose. If you do this, be sure to wrap the tape sticky side up at first to avoid damaging the suit. Duct tape won't work - once it gets wet it just falls off.
If the dive consists of sitting on the bottom waiting for others to do skills she's probably going to get cold.
Between dives It's a good idea to have a set of gloves, a good warm hat and a coat ready for wearing. A thermos of something nice and warm to drink will help to warm her up from the inside out. A second thermos of warm water to pour down the wetsuit is also a nice thing to have. Get her out of the water, put a bit of warm water down the suit, gloves, hat and coat on (coat over the now warm water filled wetsuit) and then a nice warm cup of hot chocolate and she'll be good to go. Maybe. I don't know your wife.
Edit: If you don't mind sacrificing a pair of wool socks, she can wear them under her booties. I've never done it but I hear it helps a bit.
Hope some of this is useful.