I have found that darkening the room works best. Do you have anything that you can put over the window just for the duration of her sleep? I found that when any of my three did that, I would leave them and if they were happy, they would go to sleep anyway, it may of taken 10 mins, it may of taken 1/2 hour, but they did go to sleep eventually.

You could try associating certain activities with sleep, like if you do X, then put her to bed, she knows that it is sleep time IYWKIM?