Sorry haven't read all the replies...

You need to put as many layers on the bottom as there are on top - so grab some balnkets, or a big one, and fold it up and make it under her sheets into her bed. Then whatever you put on top will keep her sooo much warmer.
We had the same prob with Charlotte and this has solved it.

Also, if you have a high shelf, away from anything flammable, put a single tea light candle there, light it when you go to bed and it will take the chill off the air - you will be amazed how much warmth one tea light can create. Put it on a saucer or something and it will be fine over night.
(ETA: We have built in wardrobes, but with no doors on them, so we put it no the top shelf of the wardrobe (there is nothing else up there))

HTH