The answer this question lies within yourself. Only you can decide if you are ready.
If you continue lie to your mother as she asks you, this could make her doubtful if you decided to tell her later. Lying has effects other than the getting out of the question for now.
Why is your mom asking you about this? Could she be concerned? She may be concerned about you and how this affects you. She is providing you the opportunity to open up to her. Making it much easier to talk about this than if you were to pop it on her out of the blue.
I personally have not told anyone outside of my pdocs and T, besides my ex-wife that tried to use it against me. This has left a bitter taste in my mouth. My mom over the past year has said some things that make me thing letting her know about it wouldn't be the best idea.
Pain is Temporary; Quitting lasts Forever. - Lance Armstrong