Good idea, especially since she is a twin and maybe just hasn't learned to sleep thru her brother (though they have been in the same room since birth). I will try this over Xmas.
The thing that's confusing is that occasionally she will nap really well, and my experience with my older daughter is that once they're overtired, they don't tend to sleep well. So I can't figure out why, suddenly, she will get a good block of restorative daytime sleep.
Babies sure can be a mystery!