Valeria is both a support and combat summoner. While most of the time she will act as a support summoner, she can do combat well against enemy commons when the situation calls for it.
As a support she can help reposition units after she moves, especially allowing some friendly units to move one extra space giving High Elves some needed reach, something you often want particularly with Arbiter of Justice. She can do it again when attacking, even attacking a friendly gate if necessary to get this effect.
She is also the best tool High Elves have against over-aggression, her combat ability against commons allows her to do a lot of damage to them, often being able to kill a common unit by just moving next to it. This makes it very hard to rush the High Elves, something many factions want to do to take advantage of the Arbiter of Peace and Arbiter of War auras.