Pleeeaasse help- promised my (short, super slim) sis I'd help her find an outfit but am stuck

[Haylstones]

My sister is getting so upset cos she can't find an outfit to wear to a wedding reception.
She bought this:
www.asos.com/Peoples-Market/Peoples-Market-Printed-Contrast-Hem-Sash-Waist-Dress/Prod/ pgeproduct.aspx?iid=547010&SearchQuery=yellow%20dress&sh=0&pge=4&pgesize=20&sort=3&clr=Yellow
but it was too big and didn't look right.
She's 5'4ish, size 6-8, blonde and in her late twenties (no dc!)
She likes slightly quirky items (see dress!) but nothing too off the wall. She won't expose her legs in a dress/skirt unless she can wear thick black tights.
Can anyone please help me help her out? Atm she is going to wear black wide legged trousers with patent high heels so just needs a top to go with them but is open to the suggestions of dresses/ skirts.

I would be so eternally grateful for any suggestions She always finds me the perfect outfits (perfect sis!) and I'd like to do the same for her

pgeproduct.aspx?iid=547010&SearchQuery=yellow%20dress&sh=0&pge=4&pgesize=20&sort=3&clr=Yellow

Bump
Anyone have a great suggestion (BTW I meant small, not short- no idea where that came from in the title!)

I always like Coast for wedding outfits. They usually have beautiful bustiers which would go with trousers, which would probably look fab on her as she's so petite.

Do you have a Jesire anywhere near you? Normally in department stores. Their clothes are cut perfectly for petites and very quirky / weddingy.