Yes, the sentence is mostly clear in its meaning. However, to improve clarity, you could consider rephrasing it slightly to "Her jaw dropped as if she had seen the devil."
No it is not a correct sentence. It should be "Her jaw dropped as though she had seen the devil."
There is no proof that the devil has ever been seen.
Ram is inept at money making since he has no job skills.
No. After all, the devil does not really exist.
Your about to die
Has anyone seen my eyedropper?He injured his eye when he dropped his eyedropper into it.
I have seen the scene.
Many people have claimed to see the Jersey Devil, however, very few photographs of the animal exist.
Anna and Marie have never seen a cattail before. However, you are not supposed to end a sentence with a preposition, so the correct sentence should be: Anna and Marie have never before seen a cattail. I don't think anyone would mind if you used the first form, though. It sounds a little better.
I haven't seen the girls all day.
A sentence starting with had would be a question: Had you seen her before that?
You or them
Barnaby Stubbins went out one night and fell into a bog. It's said his ghost can now be seen in glimpses though the fog.