PJ - if it is any consolation my DS who is 17 months has never slept well at night since he was born. We have had probably 3 occasions where we have had about 8 hours solid sleep, but even then I didnt sleep well as I was anticipating him waking up!
We usually get him to bed at 7 - in cot awake (ish) and then he sleeps until 4.30am then I bring him in our bed where he sleeps or another hour snuggled to me (where I am on the edge of falling out of bed). Then he sits bolt upright demanding milk - drains a bottle and then sleeps for another hour.
We were managing with this - not quite ideal scenario until we went on holiday last week. There he did not like the travel cot, napped at odd times (despite the best will in the world to keep him awake) and ended up having to cuddle him to sleep, put in cot and then he weould wake in the early hours - bring him in our bed, and so on!
Now we have regressed even further to the extent that he just went to bed half an hour ago - I did put him up at 7.30pm but he just screamed for us - not tired as had a late sleep in the day. He is a very busy boy - very chatty and I think his brain is too busy to switch off. It is very hard to be rational about things when you have had little sleep - and the interuptions to your evening 'me' time or 'us' time is not good for relationships. We also have a DD and sometimes I feel sorry for her as her sleep is also disturbed. I have tried CC but found it too stressful, tried the shush pat, which was partially suceeeful but now he is too big and strong and has a temper that he battles with you - I was so annoyed last night when I put him in our bed to get him to sleep - he hit me, giggled at me, pulled my face, etc - all playing - and I eventually turned my back on him and ignored him - then he went to sleep as the entertainment had gone.
No real advice to offer, but I do agree the other posters who talk about doing it in baby steps - and I do agree that the younger they are the less impact it has on them. I would go with establishing the next step in her routine - to get her used to the cot in her own room. I take it you work at least some of the week, as you say she is in nursery, and this is part of the problem as you do feel that you have very little time with them in the day. My DH is also useless when it comes to helping - some nights he is not in until nearly 9 and I have had to do the whole tea, bath and bed routine for two by myself, so that on the days that he is around, he cant tear himself away from Sky Sports to even help.
Anyway, enough rambling - keep us posted on how you get on - you definately have to be consistent and to the same every night and eventually it will have an affect - you are a good mum as you care about this and want the best for your daughter, but I know exactly where you are coming from with the frustrations