In panels 3 and 4, she doesn't have it, and in panel 1 the BFS is not visible, so it would appear she draws it between panels 4 and 5. Now, why would she want a long pommeled dagger?
-Maybe the blade is some sort of Erfian metal and very heavy, the long pommel mere acts as a counter-balance
-She is used to and prefers the BFS style pommel and has developed a long pommeled dagger style as her backup weapon
-The long pommel is meant to mimic the BFS pommel and is just for show. If she were to lose the BFS she could put the dagger in its scabbard to throw enemies off
Also, that's an awfully long dagger (I'd say almost 10") so it might be used as a slashing weapon in some cases.