Quote Originally Posted by Kraco
I'd like to note here that a kid would learn much faster to adapt to an automail than an adult that has been using a real arm for all her life already.

Still, aside from becoming a clockmaker, an arm won't slow one down quite as badly as a leg. Lan Fan can still run just as well as before. The only difference now are finer tricks that rely on hands, but slicing somebody isn't such a fine trick. She really didn't have that much to adapt to.
I'm sorry, I still say the biggest contributing factors are the fact that Ed's job was effectively "scientist" and Lan Fans job is "freaking NINJA!".