When I first started counseling, I had a lot of doctor's appointments which interfered with work. When I was working, I was doped up meds or having panic attacks and couldn't function at work effectively. I was always asked by coworkers where I was going or why was I always away from my desk. Eventually they'd ask why was I always going to doctor. (I worked at a hospital, so they'd see me waiting out in clinics' lobbies or see me carrying my huge medical record.)

I know this story has nothing to do with self-injury . . . but I think my feelings of embarrassment of disclosure are similar to your feelings.

I asked my counselor how to deal with others who ask me those type of questions that I didn't want to answer. He said, "you don't have to answer those questions . . . it's none of their business." He gave me an empowering reply to say to people who ask me stuff I rather not disclose, he said to say this:
<ul type="square">[*]"I'd rather not discuss it at this time." And he said to end it there.[/list]
I have a problem with trying to please everyone . . . sometimes at my expense. I don't have to give anyone a reason for stuff that is my own business. Neither do you.

As far as disclosing with your step-daughter, you might want to disclose to maintain an open line of communication. Maybe discuss with your hubby there, too.