Dj, I think it's always good to be prepared, and there's nothing wrong with guiding our kids. I think one last point to keep in mind is that often it's a an evolving system that she herself will fine tune the more she uses it. It will become second nature to her eventually. If she is the creative type, one thing that may occur (which has happened to me!) is the more detail you request about the design, the more constraints she may feel are imposed on her when designing the cake. So (like BakingIrene and Jason listed) important stuff like event, time, guest numbers, flavours, portion size, delivery/pick up and basic colour scheme is a good place to start, but if she wants to have some latitude with design, it can sometimes backfire if you ask the client to create all the design parameters. After all, it's the fun part of the job
Good luck with the new business!