I really do appreciate all the answers here. It helps me to recognise if my expectations are on par, or whether they are too high/too low. So thank you.
Some points to add are that I have lived with my step daughter since she was 5 years old, so for 7 years we've lived in the same house.
I generally don't 'parent' her and I leave this to her Mum, my partner.
However, I have input as we live in the same house. It would be like living in a shared house and not having a say in what happens. I do a lot of the 'housework' type things, even though me and my partner both work. My partner loves to cook and shop for food, but the other bits, I find myself doing them. I financially support my step daughter too, when she's with us.
So I guess for me, I see her Mum running around after her and I find that difficult to sit back and watch.
I've noticed a lot of comments about having parents that have separated. I was in this situation when I was little and I have sympathy and understanding of the effect of this on young children - so this has not gone un noticed. Personally, I don't think whether parents are separated or not should have any effect on how much a child should help out in a household.
I'd love to see her gain happiness and independence, and the joy of self sufficiency through experiencing a sense of 'community', and helping each other out daily, I feel it grows a certain sense of compassion and a sense of self.
She gets herself to school via a long bus journey, is able to bake cakes from scratch by herself etc so can be very independent when she wants to be.
The taking herself off and crying...hmm. Well, she's done this for a long while. It's normally when my partner says 'no' to something. Which isn't often to be fair. Even if we are having something for dinner which she disagrees with (again not often), she will go off, cry and slam her bedroom door.
I think that's her default reaction to something she disagrees with.
My partner always gives her time and then goes up to see her and discuss what's happened.
It's difficult for me to know where to put boundaries, when it's okay for me to say something, when it's not okay. Being a step parent is tough. If I sit back and not have a say in what happens in our house, it builds up in my head. If I do say something, I need to be compassionate to both my partner and her daughter. It's hard to meet everyone's needs isn't it.
I have wondered if she is on the autistic spectrum. She can be quite fixed and rigid in what she likes or dislikes. Food, taste, clothes, interests.
Anyway, thank you for your comments :)