Agree, that's not a CS scar. It's a crease mark on her tummy probably from shorts or something. CS scars are way lower than that (I was surprised when I had mine, I thought they cut your lower tummy, it's definitely not in the tummy area at all!). Also Pippa's baby is what, one? A CS scar would still be much more obvious scar than that little mark.
She looks amazing regardless. What a figure. Nice bikini too.