I cannot believe I'm saying this, but I agree with you. If she's going to be left in one half of the uniform, with vines covering any other parts that would be considered inappropriate to leave bare... then it would really make more sense for her to have the pants like the other half-naked inmates, and have her vines be thick enough to mostly cover her breasts. It would just make more sense in context, I think. Unless the shirt was made long enough to count as a sort-of minidress, I suppose. Her current outfit just looks ... off, somehow.