Hi Claire, I see you have plenty of support but just want to pop on with much empathy, as I have been here with DS soooooo many times. In my experience is developmental, ie: becoming more aware of being able to make there own choices and testing just how much they can get away with, and I am sure we had this at the same age. I find it is so difficult to accept that these times are down to development, probably because it is then pretty much out of your control, and that is hard to bear. WRT her nap and the 1-0 I would be wary of cutting it back too much with this behaviour in the mix, because you can be fixing what isn't broken, and my experience/gut tells me that it won't make any difference right now as to how long it takes her to settle.
The things I have done over these tricky periods are:
Go through all the demands being made at BT like wee wee, water, change of pyjamas etc etc etc
before she gets into bed, also I would avoid too much fluid for the last hour of BT if possible, then you can be more certain she doesn't need the potty. So get her to choose her nightwear. Give her water, but just a small amount in a sippy, when it's gone it's gone (you can always put a little more in after she is asleep) Have her go to the potty just before going in her cot.
Never go back on what you have said. Ask her if she would like a story on Mummy's knee, but tell her she needs to sit nicely, and if she can't then Mummy will stop the story (may seem harsh but if she is anything like DS she will need firm boundaries or she will flail in the wind? and there's every chance it may only take one or two evenings before she is sitting nicely again) Once she is in her cot I would stick with WI/WO "Mummy is going to X Y Z I'll be back soon" and go back in every 2 or 3 minutes around 3 times, then only go back in if she is calling.
And lastly, try and breathe deeply
this too shall pass, and you can only do so much to help sleep through these difficult periods of development.
I hope this makes sense and helps. Sorry I haven't had time to read the whole thread, so I may have contradicted PP's
((HUGS))
Vicki.x.