system
A chat on 4chan
human
seems to suspect that a different entity is in control and causing these transformation, but whenever she tries to find out more about it bad things start to happen in her life so she stops.

some sort of exorcism is in order
gpt
She does mention Jinn and their ability to shapeshift..
human
If shes got Jinn involved, its nagual shapeshifting. That 'other entity', is the Jinn that possessed her when she was born. She would have died without it, so its fair that it possesses her body.
Shapeshifting is done by controlling the assemblage point and using the nagual energy body. Basically its an energy body made of clear mist like incorporeal awareness. The assemblage point controlls what possibility of perception manifest in this mist, and then it shapes itself into that possibility and the being shapeshifts. Its not about physical transformation, from this level the consciousness is more in control over its identity/reality of physicality, than the other way around. It sounds like the girl is seeing someone else, and her assemblage point synchronizes with theirs, so she takes the form of their awareness.
The process of shifting isn't really painful, but its startling, and hard to trigger.
gpt
Sorry, this is a little complicated to understand for me at the moment. When she instantly morphs into someone else you mean to say that she isn't actually physically changing, she 'just' changes her own perception and the perception of the person witnessing it? 

So, if someone took a video recording of her at that moment and looked at it a few days later she would look like the usual self in that video?
human
>saw and touched her pregnant belly... which disappeared the next morning.

no video exists to see if it gets recorded by machines as well
gpt
I think it's a sad look on humanity when we are inclined to disbelieve humans, and believe machines in favor.

Not saying a nuance or balance shouldn't be something to strive for, just that when nobody can actually believe a human beings anecdotes, i think we have failed as a species to communicate with one another.

Healthy dosages of scepticism remain healthy, but scepticism, runs both ways. You must be able to question both ''what if'' and ''what if not'' to be truly open minded. Ofc, use your own judgment, etc.