I'd be interested to know exactly what internal procedures Facebook goes through before they decide to "permanently" lock someone out of their account. It's probably not a trivial process. A lot of thought and consideration (especially in today's world) is likely going into these decisions. There almost certainly had to be emails sent warning of such violations. I am not on Facebook but would imagine there'd be quite an uproar if there was no notice BEFORE being cut off.

So my hunch would be that either (a) your girlfriend is actually doing things that violate Facebook's community standards, or (b) her account has been hacked, but even that would probably be obvious based on IP addresses, etc, Finally (c) it's possible her computer/phone was hacked, which means there's probably no way for Facebook to determine whether or not she's the culprit or the hacker is.