Help please, sewers!

My DD came home from school today with a scissor cut in a favorite lightweight knit dress. All the material is still there, it's a maybe half centimeter wide x centimeter long triangular flap hanging there. My initial thought was to use stitch witchery (on the back) and adhere it to another similar piece of knit fabric (from a onesie or something). Does this sound like it'd work? Or am I better off trying to stitch the entire border of the cut? I was just worried the ends would fray when I wash it and it'd open back up...

Not a super expensive dress, but it was her "first day of school" dress and was super cute, so I'd like to try to preserve it if possible. Thanks for any advice!