Well, Mishin's style is go big or go home. He is one to make risks albeit calculated risks. This is a huge opportunity for him to have a female world champion to his name, having been known primarily as a men's coach, so I'm sure he will help her make a sound call.
It seems Liza just doesn't want to win by a few points on PCS, but she wants to cement herself as the one to beat. As she herself said, the 3A will be a must in the future, and clearly she wants to be one of the skaters to push that. Mao tried to do it, and established herself as a dominant force because the rest of the field was trying to get their 3-3 down, let alone 3A. Now that 3-3 is a podium standard at the World level within the field, the 3A (or quad) seems to be the next step forward.