4C

Why do you think the President’s wife had turned up?

She has someone giving her information on what Janusz is up to. She didn't just show up by coincidence.

Anna and her husband needed to discuss what was going on with his political career.

They may be romantically estranged but like a good business partner she ensures that she is kept in the loop.

She wanted to know what was happening?

All good answers

Her position as First Lady is at stake too. I’d imagine she keeps a finger on the pulse, knows what’s going on where, and has come to confront Janusz to see what can be done.
I did not believe she was there because of his affair with Sonia.

I thought it was because she's a smart person and while she figures Janusz is having an affair, she needs to know what is going on. And the fact that it's Sonia brings the stakes for her standing even higher.