Have you tried wrapping/swaddling her? Wrapping makes the baby feel secure like in the womb and also will stop her startling herself with any reflex action, and also stop her wriggling under the covers etc.
I use a wrap, which has velcro for fastening, called a Swaddle Me wrap by Kiddopotamas..avialable from Toys R Us and also online at www.urbanbaby.com.au. We used to wrap DS in a cotton or muslin wrap but after about 4 weeks he would wriggle out in the night, like your DD, and one morning I found him with his face covered by the muslin....this scared the hell out of me so I went online and ordered the swaddle wrap. I now have 2, in case one is in the wash. DS seems to know as soon as the wrap goes one it is time for sleep. At first he would protest a little bit, but now he practically falls asleep whilst it is being put on!
They recommend that you can wrap a baby until 6 months, and it stops the worry of them moving around in the cot. I can rest now when he is asleep as I know he cannot wriggle under the covers or get stuck in the cot railings. You need to sleep also and not worry, and your DD needs to feel safe and secure in her bed.
Even though my DS likes to wriggle and roll (he is 15 weeks) when he is awake and having playtime, in bed it is a different story and he lies very still with the wrap and looks so peaceful. He can still turn his head from side to side just not his whole body and loose arms and legs. Just be careful not to do the wrap too tight, so they have some movement just not enough to escape from the wrap.
Hope this may be of help for some sleep for both of you!
Kerrie, DS Keanu 14/06/07