River Island sizing?

[user2848502016]

Teen DD would like some jeans from River Island for Christmas.

Anyone know what their sizing is like?
She hasn't had anything from there since she was in the girls sizes.

She is only small, UK 6/8 and 5'1 so thinking she would need the petite rather than short length? But not sure whether to get the 6 or 8.
I could let her try them on before Christmas but that spoils the surprise a little!

Ps she is slim but has a definite waist and hips if that makes a difference

I personally find them a bit on the small side-I'm a 10/12 and have to take a 12 at least. I've had to size up a couple of sizes with their jeans in the past too (but that could be my middle aged tummy!)

Thank you! I am thinking I'll get the 8 and measure them against a pair of jeans she already has!