If you can, buy her a dog!
Dogs bring people and kids an enormous amount of comfort. Train the dog to sleep on a doggie bed in her room or like we have done, in the hallway in between our kids' two rooms!
My kids LOVE their 'guard dog' and have said on many occasion things like 'There is no way anyone or anything is getting into our house with our Brooksy'!!
Kids have these fears. Your daughter is normal. If a dog is out of the question, my advice would be to keep comforting her and going to her when she cries for you. She will only be this small and this scared for a short time. Keep encouraging her, that she will be OK. If you need to let Daddy talk to her and promise her that no one /or thing is getting in to his house or her room without getting through him first.
My husband used to tell our first 'set' of boys that if any monsters dare to come into his house that he would cook them in the oven and eat them with ketchup! Our second 'set' of boys + 1 girl, has never been that afraid b/c they have grown up with our BIG dog Brooks!!