There is always a trade off between strength and weight, when going for a thinner blade. A broader blade is stronger, but a thinner blade is lighter and faster.
For length - longer blades are heavier, for one thing. Secondly, a long blade increases reach, but for a short person, you'd have to have a ridiculously long blade to have that reach give you an advantage over a tall person (I'm a short person, and when I fence, I'm up against people 8 inches or more taller than me... if I use the longest blade available and they use the shortest, we might break even on reach... and then my arm will get tired faster). On the other hand, a fast, skilled fighter with a shorter (lighter!) weapon can get inside the effective range of the longer weapon.
On the other hand, Kate strikes me as the type (with Voron's training) to use any weapon to her greatest possible advantage.