Step1
Play-Girlz.com
Start by appealing to her girly side: outfits. Now, we all know that stats are far more important than wearing a matching suit of armor, but set aside some gold and let her purchase things that she thinks look good on your character. If you play Dark Age of Camelot, let her choose the colors that you dye your armor. Bonus for her: She'll learn some of the basic controls and have lots of fun with the "power" you've given her over your prized character. Bonus for you: Well, if you RP, you have a new outfit that matches. Otherwise, it'll just take up a few bag slots.
Step2
WoW
Next, give her something with a little more difficulty, but that she won't die attempting (nothing is worse for a new player than death). Set aside some gold, purchase all the necessary materials and let her do your crafting. Bonus for her: She gets to help you, she learns more of the game controls and there is progress, even with the occassional failure or mistake. Bonus for you: She does the boring part while you have lunch!
Step3
Next, help her create her own character. If she really likes crafting, she can make her own character just to craft something else that your character doesn't do. Later, she will have to level the character to keep crafting, but don't break that to her right away. If she really liked making outfits, she can make a new character to find new clothing for. Note: View a similar article on "How to choose a class in WoW" if she is having trouble picking. Bonus for her: She gets to start playing the game on her own, socializing, crafting and seeing what it's all about. Bonus for you: You get your account back! You also get more time to play without her nagging, since she's playing too!
Step4
Remember to play with her, especially at the beginning. She's not going to know what a quest is, let alone how to complete it and hand it in. Don't explain too much, just play and let her work most of it out herself. Teaching is fine, but remember do not take control of her character. Let her make mistakes and work things out herself. After all, you had to do the same thing to learn.
Step5
Try to get her in a good guild. Most female players stay in MMOs for the social aspect. Get her into an active, friendly guild. They will help her, they will talk to her, but most importantly, they will keep her in the game. Bonus for her: More people to talk to. More people to help her. More interest in the game overall. Bonus for you: You can step back as you won't have to help her all the time.
Step6
Lastly, remember to K.I.S.S. (Keep it simple, silly). Don't start talking about stats and talent points and PVPing right away. She has to learn the basics. As much as you might want to step in and take over how she should spend valuable spec points, don't. There will always be a chance for her to change things if she changes her mind later, but let her create her character however she wants. Eventually, she'll learn all the intricate details and when she's ready, she'll probably come to you for advice. Bonus for her: Simplicity means she will keep playing and won't get frustrated. Bonus for you: She'll keep playing, which means she will stop nagging you about your playtime!