Erfworld 77, page 71

[Wender]

Huh? I thought it was broken, or possibly stuck into the dwagon's lower jaw.

From the shape of the blade and the way she has her hand back and the pommel in an overhand grip, it looks like she has a dagger that she intends to use on the dwagon. She doesn't look happy about facing a warlord with a huge sword.

Then, when she first looks up at Ansom, she has the huge sword back. The wrap on the grip's the same as the one on her "dagger."

Consider that: Huge as it is, Jillian seems to be able to make the thing disappear, which would be much easier if it could be reduced in size; for her immediate purposes a dagger or knife would be much more useful than a giant sword that she couldn't wield effectively against the dwagon; until she sees herself against a warlord with a large weapon, at which point we see her wielding the big sword again.

Given that she is hanging by her arm with no scabbard in sight, and given that we know resizing is possible on Erf, the simplest explanation seems to be that she can will the thing to go from dagger-sized to man-sized as she requires.

I suppose that she could have a backup knife with a matching pommel, but that would require a lot of offscreen weapon-switching while hanging by one arm between weapons in invisible scabbards. It's not impossible, but it doesn't seem more obvious to me than a resizable weapon.