I've had awkward questions too. I generally either ignore the question or brush it off with a comment like "it's old". With healthcare professionals, I'm generally honest when they ask, but I've been lucky, they usually just note that it's self inflicted (and not domestic abuse) and don't push it any further.

A friend of mine who's daughter also self harms was trying to get her head around it. I told her it was a survival strategy, hence had a positive side to the motivation as a way to get through the pain rather than self destruction.
She said she could appreciate that explanation which helped her feel less frightened by it and maybe understand a little more, but it still hurts her to see her daughter injure herself.

Sending calm and caring wishes and I hope you can feel some of them.
❤️