I've used spray matte fixative
(used for curing charcoal/pencil artworks so it won't smudge). I find that baby powder dulls the wig colors and applies blotchy, so I prefer the spray matte. (Also much quicker.) The fabric sheets I've only used before when I've had a long, static-y wig, but even then I prefer Scotch Guard. Doesn't do anything for the shine.
edit: I see she's using liquid fabric softener, I was talking about the sheets that you would rub through the hair to avoid static cling. Never worked with liquid softener. Why not use an old wig and give it a shot?