TL;DR it's just perspective.
The thing with the comparison photos is that both perspective and the distance from the camera play a significant part in how large things appear.
In the old photo we're viewing her from bellow which will exaggerate the size of things. Combine this with her characteristic waddle causing her to lean away from us, making her head appear smaller and her body larger. In the new photo we're higher up, she's not leaning over and the lighting is such that it doesn't illuminate her forms like they did in the prior video. In addition to that she's wearing significantly tighter clothing cutting into her "figure" whereas the other one was more just draped across it. She's also smaller in the frame of the camera so by a 1:1 comparison she's smaller due to perspective alone.
I'm perfectly fine in believing Amber is back to her normal 500 but camera trickery is just lame and appears desperate
I did a quick little mockup comparing the two. I also adjusted the new pic for perspective because when they're sized up her upper body is actually larger than before which is just perspective distortion. My frame of reference for size was the distance between her hairline and chin and then I distorted to make the perspective the same. It can't account for all of the leaning and how it changes the position of the head but it can account for some of it.
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This isn't to say she has or hasn't lost any weight, just that all apparent changes can be accounted for by camera trickery/perspective.