Breaking a lease in California with a roommate happens. If you or a roommate moves out, you're both still responsible for paying rent as per your lease. If the person not making the payment (breaking the lease) has a co-signer, the co-signer will be contacted for the remaining rent.
Legally, all tenants do not have to be on a lease agreement in California. However, landlords should definitely consider including all tenants of legal age on the lease. There are some exceptions to this rule, though, depending on the situation of your tenant.
In CA, yes the owner / PM will want her on the lease due to laws that would protect her if she established residency thru simply staying there.
Here are the states that do explicitly state when guests are considered tenants: StateWhen guests become tenants California After 14 days within 6 months or 7 consecutive nights Colorado After 14 days, within 6 months Connecticut After 14 days, within 6 months Florida After 14 days within 6 months or 7 consecutive nights19 more rows •