Yeah, I'm still a newbie at tennis (started Fall of '04), so I can still remember the early days of doubles. Oy.
1. Make sure she positions correctly in the box and does not stay in one place. She should be in constant motion. Should be retreating when partner is hitting, moving up once ball gets past opposing net person, moving side-to-side to mirror ball, all of that stuff. No alley hugging allowed.
2. Pick a side for her to receive on and train her in all the shots she needs. For ad, she absolutely must have a BH down the line. She won't use it much, but if she doesn't have it an active net man will make her life miserable. She will also need a BH overhead/high volley.
3. As Tbini87 says, the threat of someone jumping all over at the net can make you spray balls like mad. If she has basically sound groundstrokes like you say, tell her to deal with this mentally by deciding to spank the ball and make him deal with it. You'd be surprised how you can beat a poaching net person if you just focus on hitting a good shot.
4. No lobbing allowed. As a woman playing mixed, it is so easy to get a bad case of lob-itis where you are throwing up a lob because you lose confidence in your groundstrokes, not because it is an appropriate shot for the situation. That two opponents are at net is not by itself a good reason to lob. Perhaps put her on a lob diet for your practice matches -- she can lob no more than twice in a set. And if she is going to lob, she lob the backhand of the woman if possible.
5. Have her to come to net whenever she gets a "Get To The Net Free" card. That is whenever you are about to hit an overhead, whenever you are at net having a volley exchange, or whenever the opposing team is in serious trouble (e.g. I formation).
6. Teach her to watch the opposing net man while you are hitting and start backpedaling the minute she sees any sign of an overhead about to be struck. A lot of women at my level literally just stand there, not even turning their backs or taking any sort of evasive action.
7. Guard against Service Line Creep, where she gradually moves farther and farther back in the box out of lack of confidence. Until they spin one to her feet.
Those are the sorts of things I found difficult when I started playing doubles (heck, they are still difficult!) and the things I still see in teammates and opponents that can cause real trouble.
-- Random Error Generator, Version 4.0
-- Master Moonballer