Best of luck!
Where are you applying (Grand Targhee???), and do you want to do part-time or full-time? You know this job won't bring you much money, right? Some mountains make you pay for the initial training; others train you but don't pay you for that time, and a few mountains pay you for the initial training. You might ask about the initial training they offer. Get a sense from your interviewer of where in the ski school (children's program, line-up, seasonal programs, beginners, off-piste, etc.) they would place you before walking out of that interview so you know if the placement will be something you want to do.
The ski school should want you to be interested in teaching your students -- do you have a story of something you taught someone to do, even if it's not related to skiing? Do you care about gaining PSIA certification beyond Level I? If so, tell them this, because it indicates that you may be someone who will stay beyond one season. They will want you to be someone who will show up reliably despite weather issues, teach the students they assign to you, and be willing to show up for training and put that training to use. If you have stories you can tell that illustrate these personality characteristics, be ready to tell them. If they ask you why you want the job, be ready to answer that too. If you know someone who is a ski instructor and their experiences have influenced you to become an instructor, be ready to tell that story.
Do you know if you want to teach children or adults? They may need you to be flexible about that. Some mountain ski school directors assume all women are good with children, so they assign them to the children's program. If that's ok with you, no issue, but if you are more interested in teaching adults at line-up, do talk about that as a goal of yours. But if you have a strong preference, you can tell them that as well; they may be able to accommodate your preference. They will probably have a number of days you have to commit to work, and some of those days will be holidays. Bring a calendar and be ready to say yes when they ask you if you can meet their calendar needs. Keep a record of what days you just agreed to teach and be sure to show up.
All of these things may be seen by your interviewer as more important than how well you ski.
The mountains I know are desperate for teachers. They will hire just about anyone. The mountain you are applying to may not have that problem. You may be able to tell which is the case when you are done with the interview.
