From GameFaqs:

In battle, Dagger has two main abilities: Summon and White Magic. Her summons
are ultimately powerful, although at the start of the game you cannot summon
any eidolons. Well, you can. But that's only if you over level to hell. The
least MP that a summon costs at that time is 96, and you get that much at
around Level 15 or so. Early in the game, Dagger is nothing but a healer.
However, around Disc 3 all her eidolons can be put to good use for cheap MP.
So I'm not sure what level she's at and stuff, but that might be why... I need to play IX again. :\