Thanks for the replies.
I do sleep while she feeds in bed with me. I have tried sitting up too, but got even more exhausted than putting her in bed with me.
We did not try water last night after agreeing that she feeds so much and wants it so much she must still need it. Last night she fed as she did the night before for 50mins at the 2am wake up. But she also slept till 5am insted of 4am. We have had some weeks where she will wake every hr and half!
I am going to try getting more hearty solids (she mostly been eating small amounts of fruit and rice crackers so far) and milk into her during the day and see if it makes a bit of difference

eta - i need to see what the time is otherwise I will over feed during the times she is waking every hr or so ...too easy to stick a boob in her mouth and go back to sleep. She seems to need night milk but not that much!