Evidently, the crew was capable of using the array - they were right about to until the self-destruct sequence went awry.
As for the torpedo, there would be no need for dispersal - they could teleport them right to the array. We've seen crews do this in both TNG and Voyager (later on), so there's no reason it couldn't have worked right then and there.
So... she didn't keep to it. Plus, blowing up the array counts as a violation of the Prime Directive (one of the characters explicitly states this in the scene).
As for the torpedo, there would be no need for dispersal - they could teleport them right to the array. We've seen crews do this in both TNG and Voyager (later on), so there's no reason it couldn't have worked right then and there.
Prime directive.
Even tho Janeway violated it many times she still kept to it.
Unlike Chakotay...
So... she didn't keep to it. Plus, blowing up the array counts as a violation of the Prime Directive (one of the characters explicitly states this in the scene).