Not all girls have to be pretty girly girls. Girls don't look like children forever, so Abigail is more realistic than most anime, where girls DO look like children forever. Besides, Abigail obviously isn't supposed to be a sparkly object of affection. She's the head of a family, and apparently means SRS BZNZ. So her face and manner of dressing is also SRS BZNZ. xDD I like herr~ <3
BUT THIS IS ALL JUST A GUESS LAWL
Remember Integra from Hellsing? She looked manly-ish too. o-o
As to why Abigail looks MANLY
Hahaha, Mythee, you pretty much got it down.
When Abigail was younger, she looked prettier. But the hardships of the family and her role in it has taken a physical toll on her. It hardened her not just emotionally but physically as well. I tried to portray the weight of her responsibility on her face and her manner of dress.