I went through this with my gf first and only snowboarding trip so far.
1. Let her first experience be a lesson so she starts the learning from someone else but you
2. Make sure she is on the slopes for more than 1 day, a week is probably ideal. That way she will hate day 1 most likely, but will progress during the trip and will enjoy seeing that she is getting better. 1 day trip would be the worse as all she is going to remember was that she sucked at it and couldn’t even get down a slope without falling.
3. After day 1 get another lesson for half day, then spend the rest of the day teaching her
4. Make sure you spend enough time boarding with her so she is not left along on the slopes by herself I think is the key as well as progressive encouragement. As she progresses during the first few days, she will start enjoying more and understanding why so many people do the whole snow sports thing whether it be boarding or skiing.
5. Also don’t pressure here to do consecutive days if she is broken and sore, that’s really not going to help.
That’s pretty much what I did, now were about to do a season, and she has only about 8 days on the board behind her. So still lots to learn but remembers the fun bits not necessarily the crap first couple of days.
Most importantly Good Luck, depending on the girl it could go eitherway no matter how good your intentions