There's a third explanation: It's almost certainly an accidental use of panorama mode.
- It's two poses, not three, with the stitch somewhere on her back.
- The shop attendant was taking the photos. Coates wouldn't know if panorama mode was accidentally selected for one.
- The Photos app info pane doesn't flag that a photo was taken in panorama mode. (But you can infer it from the nonstandard resolution if you know of this possibility.)
- The top of the right mirror is very slightly curved, indicating the perspective correction of panorama mode. (Not the railing, which is likely curved in real life, but the actual mirror frame.) It's barely visible to the naked eye, but you can verify by drawing a straight-edge with a lasso selection tool.
I replicated it at home with two mirrors (technically, one mirror and one iPad with the front-facing camera) and my iPhone in panorama mode, and a kitchen timer for "proof" (demonstrates over 2 seconds apart). You can barely see the panorama stitch and wouldn't notice it unless you were looking for it: https://mastodon.social/@jeff_tyrrill/111509692643373685