It's likely she will chose her own shelter but by offering a safe option she may decide to use it. Try a plastic crate laid on its side and if you can, improvise protection at the front so she feels protected. Locate the crate in a quiet corner away from other animals and traffic, perhaps concealed behind trees or bushes. Also, try to face the entrance out of the wind and rain so that it doesn't blow in. Avoid using newspaper or towels as bedding, as these easily become saturated if water does get in. A deep bed of good quality straw is warm and provides some drainage if the weather gets in. If you can, also provide a separate box for food and water, placed close by. This allows you to add more food but without disturbing the nest. Best of luck to you and your feral fur friend.