WTF is with all these people theorizing rape by zombies?
These are /zombies/ they're here to either chew on you, or in the case of L4D, pound you to death with their feet and hands. They're not here to fulfill your rape fantasies, and not to bone you to death (though that would make the Tank MUCH scarier).
If her clothes are ripped, it's probably self-induced, wear and tear from her struggle to avoid infection, or ripped during the beatdown that infected her.
No idea why she cries, but I'm sure "rape by zombies" isn't it.