Well she pretended to believe they were married and actually filed for divorce, which made him look like an absolute arse when the proceedings had to be set aside because no marriage existed. Whether that gave her any kind of psychological or PR advantage or not , who knows? She still didn’t get anything like a divorce settlement.
But her choice wasn’t legal marriage or religious non-binding ceremony. It was a choice to play along with the ceremony and play dumb or not get any ceremony at all. It took her something like 10-15 years and two children to even get that from him. He clearly isn’t too bothered that everyone can see he’s a skinflint who treats the mothers of his children terribly.
It was very choice to breed with a weird rich guy in the first place though.