let me start by saying i am by no means an excellent snowboarder, i have about 20 days under my belt, i can comfortable tackle any black and can hit natural kickers, do tree runs and starting to try double blacks and extremes. I took my wife to NZ for 4 days last year and 2 days here in Aus this year, She had never been to the snow let alone snowboarded. After her first day she was hooked. I put her in a 2 hr private lesson first thing so she could get taught by a professional. once she had the basics of falling leaf, skating and getting off a lift is when i tried to give her some help.
Basically i think the biggest thing is to make sure you are positive in everything you say, encourage encourage encourage!!! if you make her feel stupid or like she is doing something wrong chances are she will hate it. I found that another huge thing that has helped me teach my wife is that if she isnt comfortable doing something no matter how easy you think it may be, dont push her to do it. Different people learn at different rates and in different ways.
I think that the more enjoyable her experience the more likely she is to come back again and again, my wife spent her 4 days in NZ and never made it off the green slope, did i want her to do some blues with me, yeah but i knew if i forced her to take the lift higher she would hate not having full control on her way down. Everyone is different and i find that in anything, if someone is comfortable and not being yelled at or made to feel stupid, they will succeed more than they fail, hope this helps
my names's Petey and i have gigantic balls