If she used to be toilet trained, then this behaviour is probably due to stress or anxiety I’d say. Has anything changed recently in your life? Problems at home? Going back to the office? In any case there’s no point in telling her off unless you catch her in the act. Make sure you use lots of positive reinforcement when she does it in the right place though! Your sofa has to be thoroughly cleaned to make sure no odours remain. And if I were you, I would block access to the living room unless you’re able to go in with her and watch her while she’s in there.