It is great that you want to enter someone for this award. Students should do this more, not just to get their mentor to win the award, but simply to show a mentor how much they appreciate the effort.
There are some good threads on this subject.
Here is a recent one, and I had a post that explained the judging process, in
this post.
My advice would be to start early. Get as much imput and help from other students and adults on your team. You don't need to tell the nominated mentor about your plans. Also, get input from people on other teams who know your mentor.
Many nominators do not focus on pointing out how the nominated mentor communicates. That is what the award is about, so be sure to focus on your candidate's communication skills.
Good luck,
Andy B.