I'd hate to be young and worrying about popularity again.. that sucks! Your story really got into that theme well.

One tip I have.. and I hope you don't mind ... is to give your reader something to see, taste, touch - to ground them in reality. That helps them see the situation and enjoy it, and would have helped structurally with your intermission. For example, you could have started with that, exploring how she felt though her actions.

Eg

Kate's clothes were scattered over the bed like her thoughts. Would the pink dress be too much? Too short? The one with the sequins reflected her own face back at her and made her stomach flutter. Both were old and frayed. She slammed the cupboard door and sank onto the cold floorboards.

She felt like a shadow in their midst, it was as if they could barely see her.

This was my favourite line for the beautiful visual image and feeling it conveyed.

Keep writing!