Can someone PLEEEEAASE finally sack the person who does PR for Kensington Palace?! Things are going worse in ways that nobody even imagined possible.
Graphic designer here and I personally think the Photoshop edits are innocuous but extremely disastrous considering the context. The edge of Charlotte's sleeve is typical of a "clone brush" or wrongly blended copy-paste which is used to move elements around to create more space. This meant Kate's hand was either Photoshopped in, enlarged/rotated, or the grass on the other side of Charlotte's arm enhanced to make it greener. There could also have been a mistake with the Layer visibility which meant the corner of the sleeve covered the obvious error was mistakenly made invisible.
The edits were most likely done to fix compositional errors. I think the most likely explanation was that they spliced minor elements from another picture taken at the same time into this one because everyone's face looks the best. Kate's hand may have been at an odd angle where a finger looked missing so they replaced it with one that clearly shows her hand at a visually pleasing angle. Looking at the position of Charlotte's arm, I also think it's possible the original shot had her arm going out of the frame. So they copy-pasted another arm (obviously her own from a different shot) just to make the composition more pleasing. The elbow seems curved at a slightly awkward angle and incidentally fits "perfectly" inside the photo allowing for a visible strip of green grass. This very convenient posture that runs almost parallel to the edge of the cropped image is bit of a red flag for trained Photoshop eyes. At the very least, it looks like some Liquify was used on the outer edge of her sleeve. (This is when you nudge the outer edge around to customise the shape of one area).