You may have had concerns about the case or the advisability of litigation, which can be difficult to communicate to the client. Talking with the mediator can be a helpful tool to start these conversations. Mediators employ a tool called reality testing to help parties consider options.
It may well be that is in your client’s interest to have a negotiated settlement. Although you may have negotiated with the other side, it may have been relatively adversarial. Working with the mediator can help with generating more creative options and also presenting them to the other side.