Rachael sorry to hear that things are still not going too well. I agree with Vicku that maybe you will have to accept that she is always going to be on the lower end of the sleep scale and try to work with it. That is pretty much what we have done and believe me I totally understand how you feel and that you can't see a way to make it work to ever get a better routine going. As you know we are still having bad days but it definitely has improved overall. I just don't think my lo will ever be consistent - she is out to shock thats for sure. Anyway, we did start slowly moving out the nap every few days to see what she could cope with. I still doubt myself when we get bad days and think its due to being OT and maybe it is but she still had bad days when she going to bed very early and having naps earlier too so am just going to have to live with.
Anyway, although you are depairing of the situation right now I am sure that things will improve for you. This week we have had 7am, 6.30am, 6am, 5.40am, 5.20am and 6.00am wake up times so as you can see she does not have a set pattern at all but I am definitely more relaxed about it and just do the best I can to get her to sleep, unfortunately, she is not as keen as I am to make this happen!!
Sending you lots of hugs, I know its probably no good to say this but please try not to stress about it so much, I know that their sleep becomes the sole focus of your day and for me the wake up time can set the mood for the day which is not good and they probably pick up on it.
Lots of luck whichever way you chose to approach it.
PS - do you get to have a lie-in on a weekend , dh and I take it in turns so I sleep late on a Sat and he does on Sunday so we both feel a bit better.
Hope you do have a good weekend
xx