Olga's role in battle can be defined by what enemies she is facing due to her ability to absorb enemy skills/traits. In the demo she will largely be a support character who makes effective use of her minions to support the party.

Recommended Passive Skills:
Stay - saves you summoning a minion for the next battle.

Recommended Command Skills:
None in the demo. Stick with Attack, Defend or Escape, Monster Tech, Summon and Items

Skill System:
Tentacle allows Olga to gain a skill or trait from the enemy she used it on. She also has three unlockable skills in the demo:

Natural Cure	Use tentacle on Seedling, Treema and Fungi Fiend (not in demo but alternate method: use on 10 different enemies).
Summon Lucky Cat	Use tentacle on Lucky Cat.
Stay	Use tentacle on 5 different enemies.

Of her, summons Lucky Cat is probably the most useful, with its relatively high damage output and ability to heal party members. You can use Slime if you prefer a damage dealer who can survive more hits or Cube Slime if you wish to protect the party from attacks.