Better to deal with this problem Now than later...obvously...She cant sleep, she probably isnt lieing...Kids are known to be afraid of the dark, and such things, Maybe you need to teach her about Fiction and whats not... Give this a little time...Punishment isnt best option...
I think the husband has only slept in the spare room for the last two nights so that everyone could get some solid sleep.
As for the manipulation - I believe it is entirely possible. My 3 yr old (almost 4) often manipulates me. For example: She will complain of a stomach ache, to the point of crying and laying in the fetal position, then once a family member or friend comes in whom she adores, she miraculously recovers. And thats only ONE example. There are many. Smart children, such as this eight year old and my daughter, who, for attention or just to please themselves, manipulate the situation to their advantage.
In my experience, when I believed she was manipulating me, she was. If you feel your daughter is doing that, she may very well be. Who knows their children better than an actively involved parent?
I doubt that she is manipulating you, if she has stated she is scared there is no reason to believe otherwise. Fear of one thing or another is often the cause of such behavior. Try rearranging her room, giving her the freedom to set it up the way she likes. Let your daughter choose some colors that will help her feel at ease. Change her bed...move it to another location, add an additional pillow (this will make her feel less alone,) a softer comforter. Reassure her of what a great job she id doing in setting up her room the ways she likes. Giving her a sense of independence and control may help to make her feel more independent and that this room is "her place."
I do not know the reason your husband sleeps in the guest room, but your daughter may feel that she is winning your attention over her dad's...
In a certain sense, it's not critical to make a determination about the validity of the stated fears. I say this because, 'real' or not, if the beahavior is to change it will rely on your being steadfast in setting and adhering to the limit that your daughter go to sleep in her own bed and remain there. No doubt for a while this will generate an unpleasant reaction, but it won't get better if you relent and permit your daughter to sleep with you. Now, if you want to be thorough in evaluating her condition, arrange for a consult with a pediatric mental health professional and also be sure to talk this over with your daughter's pediatrician. Sometimes, but not always by any means, pediatricians employ short-term use of an over-the-counter medication such as diphenhydramine hydrochloride (Benadryl) or a medication such as melatonin to both induce sleep and help the child stay asleep during the early phase of the change plan.