It has nothing to do with Twitter and probably nothing to do with facebook.
Marbox, if she 'uses' facebook, then she's using a browser, the internet, etc. Are you seriously saying she doesn't use email?
The problem with facebook isn't facebook, it is the third-partly applications. Opt to install one and you've just granted access to install stuff on your system. If you aren't cautious about the apps you install, you may end up installing one that carries a trojan.