Doctor Tot give her most of the stones before her coronation at the start of the disc. The voice thing varies but in my recent playthrough she screws up more than I am willing to forgive, almost every other action in my playthrough.

This still doesn't change the fact that Ifrit and Shiva don't become regular summons until Disc three and you are almost a dungeon away from the Octogon Rod that makes Vivi get -aga spells that put these summons to shame especially since her summons need Boost in order to work fairly often. You are also getting much better equipment for Amarant, Freya, and Steiner who all can consistently out damage Dagger.

Eiko's Carbuncle is the only one that does (which create four major affects like all party haste or protect) it but seeing as how she also gets Phoenix and it occasionally activates when the enemy kills your whole party, whereas Dagger gets some powerful summons that seriously need special abilites to keep them in league with the rest of your team. Vivi is just a way better alternative to causing consistent elemental/non-elemental damage. Eiko also has a better tTrance that is immediately useful while Dagger's basically makes her do what you wish she could do normally and its special feature is lost since most battles don't last very long by the time she gains variety in her summons.