Although there are both elves and white dragons in the Hidden Forest... considering how the Mithril Elves fled to other planes to avoid the Crown War, we can tell they're not adept fighters. They're the type of High Elves who are heroes on their own but worse than bears in group battles.
As for the White Dragons... known as the scoundrels among Chromatic Dragons, they only excel in advantageous battles. When facing an invincible enemy, their first instinct is to flee, the second is to beg for mercy. Those who fight to the death are usually either completely brainless or mother dragons protecting their offspring.
These guys are not to be relied upon, so Hill can only entrust the task of protecting Edna to the Undead Tribe... even if he doesn't care about what happens to the little girl in the future, Hill absolutely won't allow anyone to run wild on his territory.
Edna leaving on her own to court death and being captured in his territory are two entirely different concepts.
