Thanks for your advice guys. I don't think kikopup's method would have any effect in the immediate future with Chevy- she will stop when I stop but she most certainly won't come back to me just yet. that's something I've been trying for a while. Treats don't really have any appeal to her when she's on the lead too but I reckon we could get there after a while; like kikopup's vid says, she needs to become more aware of me. I have been using a verbal command 'uh uh' that I think cuts through to her when she's in her pulling daze, that seems to be helping.
As for the sitting- that's something she already does so I'm not concerned with reinforcing it. She is a fairly big girl, much bigger than my toddler, so the fact that she immediately sits at most things is something I'm pretty cool with.
I think both methods used together should have some effect; I have to get her walking with me first, not just reward her walking with me etc.
Thanks for the help, I'll keep you posted on how we go!