I don’t like half the advice given here. I won’t appeal to your conscience or guilt trip you into telling her. You should tell her because it is in her best interest and you should tell her to approach the Women’s helpline or NGO to sort this issue out. I had a friend who had her morphed pictures leaked online and being her friend, I knew how distraught she was. But in the long run she says that atleast she knew and could do something about it.
Also guys. Please don’t share nudes of your loved ones. IF it were to happen to you imagine how you’d feel. Now 10x that. That’s how bad it would be for a woman socially.