I've just been served with a summons for an intervention order application. I'm needing to go to court on 7th March. The application, made by my ex-girlfriend, is making claims that I physically and sexually abused her during our relationship, and I "don't like to be told." This never happened, and I'm not the sort of person that would do this. She also claims in the application that I am "mentally and emotionally unstable". She also claims that I abused her mother when she asked me about not paying board. I always paid board when I was living there, in accordance with what was agreed. I never abused her mother, but it was, in fact, her mother that abused me, and that was the reason we moved out, as well as me staying at my brother's house before moving out because I was too scared to live there. I have been told by 3 different people that I should respond with suing her for defamation. Given the information above, is this actually possible for me to do this under Defamation Law?