It’s a known issue ... when sent to a non-Apple recipient... it has to do with the orientation of the iPad/iPod/iPhone when the photo is taken... the photo sometimes does not get auto-rotated to the "correct" orientation.
To test this, take two photos of the same item. Take the first with the iPad the way you do/did and send it. Now rotate the iPad 180?, take the photo and send it to the same recipient. Then start taking photos with the iPad in the orientation that sent the photo correctly.