I'm a therapist, and actually... sadly... this is pretty normal. Comments here are correct: parents don't like feeling that they failed to protect their children. Also, it's a very powerless feeling. But more than that, our responses to the hurts of others are rooted in our own experiences. If your mom's culture or family deals with tough stuff by ignoring it, then she probably truly does not know how to respondnd even if she wants to be supportive because no one ever taught her. Also, at least 6 out of 10 females in the United States are molested, which always makes it extremely likely that news of sexual abuse is triggering memories and pain for the person receiving the news. This may be happening to your mom, especially if she has been taught to minimize these kinds of things.

So the short answer to your question is yes, this response is quite common. I would recommend taking some time to figure out what it is you actually want from your mom right now. From your post I don't get the sense that you are in severe distress from your past trauma and that maybe you are just ready to break the secret. This may be a big relief to her. Or maybe you do need to tell your story and it's time to do some healing. If she isn't in a place to help you herself, respect this and ask her to help you find help from a therapist. (A therapist could also facilitate some conversations between the two of you.) At any rate, figure out what you need, then tell her clearly; this will help her feel more in control and allow her some ability to protect and care for you in this process.

Having said all of that, this is about YOU, not your mom. Please, don't let anyone minimize your experience or make it about them. If it's time for you to talk, talk until you find someone who will listen. It's sad if your mom can't handle it right now, but it's ok. You have different realities that should both be respected even if it hurts when they don't blend. Don't let her hurts keep you from healing.

A little confusing..