The point isn't that someone deliberately photoshopped out part of Charlotte's shoe or whatever to highlight that it's been photoshopped- the point is that there are a few bits of the photo that don't look quite right (I agree that the material on the skirt is a pocket, btw, and the shoe might be a tassel, although we can't see the right part of the other shoe to compare). But there is something definitely a bit odd around her wrist.
I would imagine that all the photos we see of them are subtly touched up, and this one has been photoshopped a bit more than most. I do find the idea that the photo must have been taken last week because Prince William says so a bit weird. You can say anything, it doesn't make it true.
If Kate wants to be queen one day, she has to accept that comes with a pretty high level of public scrutiny. If she and her kids don't want that, there's an established way out... They live an extremely privileged lifestyle at out expense- they can't also have an expectation of complete privacy as well.
I do think there must be something about the surgery that they don't want to share- whether it's a hysterectomy for whatever reason, or plastic surgery, or something else.
Does it really matter in the grand scheme of things? No. But ultimately she chose this life and the level of scrutiny that comes with it.