Don’t see how anyone would interpret an e-mail like that as creepy, or be worried about a potential stalker if that was the only message sent.

Look, you might think that it’s better to let the girl be in the dark about that, but I think it would be disgusting not to let her know. Lives can be ruined with that kind of stuff, and if the video indeed has gotten 2.3 mil views it’s just a matter of time until someone she knows stumbles upon it. The fact that OP found it (without even looking for it) says it all. Not telling her about it is unethical imo.

If she knows about it => No harm done If she doesn’t know about it => she can get it taken down