I completely agree.Her current diet isn't balanced and I'm worried about her development. Just the juice from canned food isn't enough to add the necessary vitamins. Lack of taurine can lead to heart defects and blindness. If she's unable to switch to canned kitten food, ask the vet for a supplement recommendation.
Use that playpen and put her in it while she's eating, with a towel, as suggested, so that she can't see what the others are doing.perhaps feeding her alone in a smallish carrier with a towel over it could help her focus.