For a first effort, this story is fine. I like that you set up the reader for just another nightmare-that-isn’t-real story and then throw in the evidence…that the door indeed had opened. But I think there is not enough information. She might have dreamt it, of course, the door could have blown open and she could have closed it in her drunken or sleepy haze. If there had been a big creature of some kind, he or she was a wimp. Didn’t do anything. The frightened part is OK, although you could have milked it a little more. Everyone has been home alone at some time and heard scary noises. The reader can relate to that. Maybe it is me, but I would have liked some more horror-fear-action. “She woke to find her clothing ripped to shreds on the floor.” “She felt something warm and wet — blood! on her nightgown.” “She crawled to the bathroom and in the mirror saw large gashes, like from an animal’s claws, streaking down her back.” Maybe I just like more graphics!
This is my humble — and hopefully gentle (but not necessarily gentile) opinion.