Ambiguous Disorder: Leah is called "a lunatic girl", and her behaviour does seem a tad odd, though true to the time period, it doesn't get anymore specific than that.
Deuteragonist: She's not a protagonist of either novel, but she is a central character, integral to the story. Some editions of Murkmere depict her on the cover, not Agnes.
Half-Human Hybrid: Leah is one of the avia, which would actually make her three quarters-human, but you get the idea.
Happily Adopted: Despite being the Master's ward, they are as close of biological father and daughter.
Impoverished Patrician: She is first in line to inherit Murkmere, but as fancy as the old place is, it's is very bad repair.
