Oh, boy. Where do I even begin. Let's start by figuring out what she's talking about.
I don't do paranormal debunking on a regular basis, but on the weight of some Google searching, I'm gathering that a "positive sighting" is where you think you see something that shouldn't be there, and a "negative sighting" is where you don't see something that you should.
Let's start with the negative sightings... not seeing something you should see... oh, optical illusion? Refraction of the atmosphere? You're an idiot and are looking in the wrong place? Seriously, it depends on what's missing. Moving on.
As for positive sightings, where you are seeing something that shouldn't be there, there are a number of possibilities. One possibility is that there is actually something spooky there. However, this is certainly the least likely possibility. One can only conclude this with some really solid evidence, or because you've managed to eliminate all the more likely possibilities. I can think of at least a dozen more likely possibilities, and one of them is that your mind is playing tricks on you. Without evidence to the contrary, one can't really eliminate this (more on that later), so evidence is a necessity for demonstrating a positive paranormal sighting.
One of the most obvious possibilities is that the sighting is a hoax, but of course, this is less likely for some random occurrence than misinterpreting something genuine. However, in light of the possibility of the hoax, it doesn't need to be a hoax perpetrated by the person reporting it. So, suggesting that this woman is a liar is not necessary to conclude that it's a hoax. Nor do I have to conclude that she's an attention seeker. She could really believe she saw something weird. That doesn't mean that a paranormal explain is the best one.
Okay, let's assume it's not a hoax. What else could it be? Well, like I said before, she could be seeing things. This doesn't mean she's hallucinating necessarily. It could be that her mind is doing that it does best: matching patterns. And sometimes patterns can be found where there is nothing going on. Ever seen a boat in the clouds? Or a rabbit? Or anything else? That's what we're talking about. Taking random shapes and seeing something that isn't actually there. This phenomenon is called pareidolia. More generally, this is a type of apophenia. Our brains are configured to find patterns. Apophenia generally is our brains just working a bit overtime. We see something random and our brain is working overtime to try to make sense of it. That doesn't mean the trick of light is really a ghostly apparition. It means it's light and shadow that looks vaguely in the shape of a person... and someone else might see the same thing and see something else entirely. When we see things and recognize them for what they are: an interesting trick of our brains, it's fun and a sign of creativity (not necessarily insanity). But when we fool ourselves into thinking the patterns we see are "real", then we just look like fools. Just another instance of a theist pretending fantasy is reality.
The problem here, even more generally than everything else I've said, though, is that the existence of the paranormal (UFOs, ghosts, even ESP) does NOT prove the existence of god... certainly not an all-powerful, all-knowing, eternal god.