Goofy or regular?

The team are taking their first trip out together to Megeve this week. We are taking along a few friends, two of which are sisters and first time boarders!!! Its funny, I'm sure they'll be secretly competing with one another!! The older sis is deliberating whether she'll be 'regular' or 'goofy'!! I used the traditional method of catching her off guard and seeing which foot she put forward....it was her left foot, but she's adament she should be goofy - as she kicks a football with her right. Any ideas guys??