MY skillset for my grandmaster is the following:
Lifetaker (50% HP restore when enemy is defeated)
Sol (Absorb HP equal to half damage dealt)
Pavise (Halve sword/lance/axe/beaststone/blight damage)
Aegis (Halce bow/tome/dragonstone damage)
Limit Breaker (unavailable for you since you miss that DLC content)
I guess you can use galeforce there?
I also like the Solidarity (+10 avoid/critical to all adjacent allies) and the pass (speaks for itself, pass through enemy lines) skills.
I only use the galeforce skills with flying units, so they can do hit and run strikes to enemies not reachable by ground.
I like this set, because it makes her strong enough when paired with her husband (my grandmaster is a woman) can function like a general. Block of weaker units. With this set you can also solo, paired with your husband) the 3rd quest of the DLC to get the Limit Breaker. Then you might want to use swordbreaker, cause they are the worst damage dealer to mages/grandmasters.
I BTW made Virion a dread warrior, because he has a fantastic magic stat. Because he is married to Cordelia, he has to be the frontman, flyers are to weak for me. Shame, cause he is a fantastic bowuser obviously. My Cordelia is now a Dark Knight though, some units are still gathering skills, she will definetly end up a flyer)
Lissa is my strongest flying unit, she is a Falcon Knight with this list:
Lote`s shield (DLXC content, protects against bonus damage)
Relief (+20% HP when no enemies are near)
Galeforce
Limitbreaker (duh)
Miracle (protect against lethal attacks)