Advance Wars 1+2: Mission 15

The Sonja missions kick off with Max taking the first one. Sonja will prefer to fight in the fog as her passive gives her increased vision range and her power lets her see through obstacles. This means outside of fog, she is a pretty lackluster CO (usually regarded as worst in the game), and that is before you factor in her bad luck. Later games will give her some additional tools, but she still leaves a lot to be desired here.

As for the mission, you just need to leap frog into cover, and when she is ready to use her power, feel free to just lash out at her as she will see you in hiding anyway. The annoying part is that she stocks on indirects like Grit, so there will usually be terrain stopping you from making a straight line to her. You may need to deduce where her units are through triangulation, and try to stay out of their range, especially on her power turns.