[¯|_(ツ)_|¯]

I think that lying probably isn't the way to go, since if she does end up finding out or the self harm gets worse, she probably will be upset to hear you had lied.

But, I do think you should be honest with her about this. Let her know a bit about what self harm means, such as that it is a way to cope with what is going on around you. You can explain a bit about why you do it if you would like to, or at least tell her a bit about why self harm is helpful to you.

But, you can also let her know what you need from her. For example, explain that you don't want her to constantly worry and that you want her to treat you normally, but it would be nice to have support sometimes. Let her know this isn't something that changes your personality.

All in all, just be honest! You can do this.

-Dez