I can't imagine how difficult it must be to have such a strong trigger. I definitely understand the temptation but puzzclar is right - think about what it could mean. You have been extremely strong until now. You can get through this.

Also, is there help you can seek for your sister? Even if you can't personally talk to her about self-harm if its too much of a trigger can you encourage her to reach out to someone?

Thinking of you. Please keep posting and checking in when you can. Sometimes just having somewhere to talk can make a big difference.