I was in the position you are and gradually realized I was grown and gone and living my own life and therapy was important to me so I at least mentioned it to my stepmother (who was the cause of my being in therapy in the first place!). I didn't go into detail but realized that I approved of my therapy so her dislike of it didn't make very much difference anymore; I was taking responsibility for myself and that was that. It reminded me a bit of when I went out to start my own business, quit my job first and she was extremely negative, flat out told me, "don't come asking us for money!" and was sure I would fail. She'd been raised in the Depression and the idea of quitting a "perfectly good" job was foreign and frightening to her. But I had to (and did) live my own life and the bottom line was whether I alone approved of it. I found it quite freeing to realize what my stepmother thought was literally of no more use to me; I couldn't make her love me more and if she loved me less that too didn't have much effect.