In the flashback of the party, she wasn't actually shown talking to anyone, or dancing or having a good time...
I disagree. It was a shortish flashback, we did see her smiling, greeting people warmly, baseline happy. We didn't specifically see her dance, but she did mention she did, and her ex sure as feck mentioned her "cavorting" (i have to assume that included dancing).
She wore makeup and was dressed nicely for the occasion; not like a puritan, but not with a hemline that her age couldn't handle.
None of the exhuberance of youth, and I'm sure a fevkuva dent was put into her mirth by seeing Ian and his GF (whom i believe was OW). But she didn't seem to be unhappy. Just, like, not what Daily Mail readers assume is the only believable rape victim.