I am not an attorney, I do advise you to double check my answer with a real estate attorney. If you'd like to talk to me some more about this or get a couple of referrals to RE attorneys, please email me directly, as i don't look back on this same Trulia thread for answers after mine.
Realtor Since 1996
Main Street Realtors
Try these links:
Read this first: http://www.dca.ca.gov/publications/landlordbook/catenant.pdf
Then check some of these out.
IS she living in your own home, or is this a unit you rent out.
Refer you your state eviction laws on RentLaw.com or refer to a local legal aide group.
First, reporting any threats, violence, or disruptions to the police should be an immediate consideration. Secondly, as a renter it is reasonable to expect that living conditions would be reasonable. It would seem that your landlord should be able to advocate for you and the other tenants. Sometimes it's best to present your concerns as a group a opposed to as an individual. Problems presented as a group often get quicker attention.