[KathieK]

Ideally teambuilding is done during the pre-season so that when the Build season arrives you have already worked out some of these issues and are working together as a cohesive unit. But in the real world that doesn't always happen. It might be worthwhile to take one of your build days (please don't yell at me for suggesting this!!!) and make it a "mandatory" teambuilding day.
Take the first hour and in a facilitated discussion, air your differences. That means one person has to lead this so that everyone gets a chance to speak.
Take the second hour and discuss team organization. What will the structure be? How will decisions be made and who has final authority (this may be your teacher advisor simply because you are a school-sponsored club)? Assign someone the task of writing a team handbook after build season is done (if they can't fit it in now). Having clear rules makes it much easier on an organization.
Take the third hour and do teambuilding exercises (read the Team Organization forum on CD for ideas). Stress working together positively. Do all the team members know each other? By name? Do you know each other's interests? Start with ice breakers if you need to learn those things and go on to problem-solving exercises.
Vow together as a team to move forward and improve the organization for the benefit of future years.
And if you only have one mentor, find her some help! One person cannot possibly do all of this and that could be part of why she expects the seniors to pitch in as mentors.