After she was able to enjoy the hospitality of this Vicomte previously without any ado and only short reports on her attending the French Open with him, she in all probability could not foresee such an occurance.
She couldn't, despite attending a ball that had more than enough debauchery to make the son of a dictator blush? If she didn't see them coming, see this coming, then I am sure that she doesn't know these poeple as well as she thinks she does.
Most probably they didn't feel they have to accord a "Miss Middleton" the same respect and protection they would accord a "Demoiselle du Faubourg-St.Germain".
Which is why it is important she be made to realize and accept taht she isn't one of them, one of the aristocrats and that she can't really get away with these things or be treated as well an old blood female aristocrat might.
I personally see Pippa as the victim of these French guys.
She should not at all have gone there, not knowing them as well as she should. Don't our families warn us about going off ot foreign countries to hang with strange men that we might not know well, if at all?
I believe she now will make up her mind about her future and she surely will listen to William's advice.
Well, quite frankly, he should tell her (and she should listen) that she needs to let go of this climbing and scale back her expectations and requirements in regards to what she might think is a suitble match for herself.