Hi Kandymouse
It sounds like you're having a really tough time at the moment.
Lack of sleep is a real killer, isn't it.
Your DD is finding it hard to make the transition from co-sleeping to sleeping on her own in a big cot. That's really not surprising. It must be cold and lonely in comparison to the warm safety of mummy and daddy's bed.
It will take a few days for her to get used to the idea, but she will eventually.
In the meantime, there are a few things you can do.
For example, you can put her in the cot sleeping across it, not length ways. By then adding some bedding etc beside her you can make her sleeping space smaller, cosier and less daunting.
Do you put her down in the cot for daytime naps? That could help her to get used to the cot as her new sleeping space. Daytime naps are often more relaxed and casual than night time sleeping and there may be less pressure from you for her to sleep urgently. Of course it doesn't matter if such naps are comparatively short either.
You can also put her in the cot during the day to play so that she feels at home and comfortable in there.
It really seems that babies are so stubborn when it comes to sleep. They will sleep any time any place when they want to, but when they are determined not to sleep they have amazing stamina.
However, she will get used to it soon and when she does, you and your DH will sleep so much better. This short (feels long!) time of struggle will seem worth if for the gain in the long run.
I'm sorry if my advice is all obvious and things that you've already tried, but I thought you needed a positive and supportive reply.
Good luck!!