Oh, the clothes-tug! Never a sign of a well-fitted garment. 🙈
Even if Meghan was buying off the peg, she could have got a tailor to alter it - or, I'm sure that VB's people would have done it. Considering that Meghan's wedding dress had that similar bad fit, I think it's Meghan insisting on that tightness over the hip. She must think it looks best that way. It probably does look good when she stands perfectly still with her feet together, but the moment she moves, it rides up and gets stuck. Then she has extra material in the torso (like in her wedding photos) because the dress has rucked up as it's too tight to slide over her hips.
When I saw a photo of her wedding dress on display, I was surprised how beautifully shaped it was. It didn't look like that on her at all. I think it must have been that tightness over the hips that she favours which ruined the line.
The VB dress photos are also a good illustration of why you should wear a slip. I know they're old-fashioned now, but they make clothes look better. My late mother was really good with these details. A slip lets the material skim, (assuming the dress or skirt isn't too tight), makes the fabric drape better without catching on your legs, stops static cling, and smooths out any panty lines. Not that Meghan had panty lines in that blue-dress pic, but a slip might have helped the fabric look better. It's clinging, which makes it look a bit thin.