Hopefully some people will stop believing what someone says without providing evidence solely because it is what they want to be true.
I don't think it's possible to prove a hack. Anything can be faked.
Anything can be faked, but that doesnt mean there wont be evidence either way.
I would also point out that it was not necessary for the hacker to change bitcoingirl.clubs password to achieve what he achieved.
If the attacker was able to install a key logger without user interaction, he could have run any arbitrary code, including code to open a headless browser to view bitcoingirls PMs. Changing passwords alerts the victim of the hack and causes the victim to try to lock down their accounts.