For those who like closure, this is what our troupe settled on.
In the near term, my maga will be making and using this spell:
Graceful Flight of the Unfettered Brand (ReTe 25)
R: Voice, D: Sun, T: Ind
Causes a sword, knife, or similar bladed weapon to take flight and hover near the caster. At any time during the duration, the caster can cause the weapon to move as she sees fit. For as long as she maintains concentration, she can use her Perception + Finesse (plus the blade's normal statistics and quality bonuses, with a Strength of 0) to attack and defend with the weapon at a distance. The blade counts as being engaged with an opponent, preventing him from simply running past it to attack the caster. When the caster ceases concentrating, the weapon reverts to floating at her side.
(Base 3, +2 metal, +2 Voice, +2 Sun)
In the long run, she may be creating an enchanted item that generally follows the guidelines given by ezzelino above. Our troupe is fine with allowing a sword to attack in a straight-forward way that doesn't use skill, but rather agility and speed. They're more of a high-fantasy loving group than I am, and they come at it from an aesthetic and mythic point of view more than from the game mechanics and balance end of things.
However, I am really quite taken with the image of my maga training the blade to attack, heel, and so forth in the covenant yard. I really like the idea of her playing fetch with it, and of it being able to act on its own. So, I'm quite likely to go with the expensive route and actually use the spirit of a well-trained guard dog to give it some autonomy.