Cute & comfy but the sizing wasn't exactly right

It's cute and super comfy but the sizing is off slightly. I got a L for my size 10/12 daughter which is what it said to do via their size guide. It's HUGE in the waist, but fits everywhere else (length, arms, bust etc).  On the model it tapers in nicely at the waist, on my daughter it doesn't at all. She paired it with a waspie type belt and it looks cute like that, but otherwise it's just way too big in the waist. 

Material and quality is nice, colour is cute. I worry that if I got a M for her, it would be too short and too small in the bust.  Very nice dress but note that it will be larger in the waist then pictured.