Found out that my little sister cuts her arms? Help?

[“Mick”Mick“]

It's a call for help, she won't tell you directly but tells you indirectly on Twitter, you need to tell your father and show him the evidence of your sister's self harm, make him believe, if you really believe your father won't listen, then you need to tell a relative.
Cutting is bad enough but if your sister doesn't get some form of help it will get worse to the point she will cut herself for the final time ever.
If you love your sister or not, be a caring human being and do the right thing.