Sending loads of I feel for you and your DH. Does your DD have any sleep through the day? Does she have a sleep in the evening? Does she like any toys that she can play with when she is awake, but will keep her amused in her cot? Is she on the bottle? If so there is a forumla in the Novalac range that helps with sleep called sweet dreams, if you want to have a look at the website . The only reason why I know about that ones is I have seen it before, as I buy the Novalac constipation one for my little V.
I know some little bubba girls dont like the dark, when they are awke, so if you have a nightlight maybe that might help. However I know with my little V if she sees the light on at night she tries her hardest not to sleep, so I need to have it darker for her, whereas my older two dont like the dark they like to have some light. Thankfully I have a dimmer so it helps my older two, but doesnt affect bubba V so much, however I still need to have V facing away from it.
For her bath have you tried the bedtime bath, sure its Johnsons & Johnsons brand, as well as giving her a bit of a massge when putting moisturiser on her skin after her bath, before her bedtime.
I hope some of my ideas help, GL hun.