The problem I have had with my lgd is that mine always wants to be able to see and hear what's going on so he won't sleep in any sort of house. He will consent to go into the lean-to on the side of the garage if it get's really cold, like below zero, or windy but otherwise he stays out where he can see things. Usually that's out in the middle of the highest point of the driveway. Since he's getting up in age I am going to get him a heating pad and put it in the lean-to just in case he wants it.
I'd just provide a few sheltered places and let her use what she wants. Does she mind being where she can't always see what's up, does she have to see everything? Her personality may define what sort of shelter she'll use.
Nevermind. Just read through the thread again and saw that she does have a shelter already. Sorry! If she's seems fine with the blanket that should work but it probably wouldn't hurt to stuff it with straw so she can burrow into it.