Do you have a bicycle? Maybe you can take a long ride and sing while you're cycling? That's sort of private.

My SI method of choice is to and sometimes it helps to write those words on my leg instead. (Whiteboard marker is my preferable method - waterproof markers are really hard to wash off)

Also my parents are starting to trust me again (for example, they'll dare to leave me alone in the house overnight, which they didn't dare for a long time) and I'm afraid that if I SI and they find out, they'll start to thread lightly around me again, and I dislike that for their sakes - they should have more of a life than worrying about their daughter 24/7. So that is a great motivation to not hurt myself.