Tenant's guest causing problems

[Alicia Calderon]

I have a situation I have been trying to research to make sure that I am doing everything correctly, since this is my first rental property and I am brand new. I own a duplex and live in one side and rent out the other side to a tenant who has been fantastic thus far. However, recently her daughter who is over 18 came to "visit" and has only been there since this past weekend. First, her daughter was arrested for a fight with her mother (my tenant) the other day. Second, I found out that her daughter is a recovering addict whose sectioning was denied. Third, the tenant stated to me last night she apologized her daughter getting home last as she suspected that her daughter was no sober and stayed away. This has all been less than a week. 

I do have a clause on my lease about guests and all people living there need to be on the lease. I am worried about fair housing laws. I know they cover current illegal drug use and that technically she isn't a tenant as she is not on the lease. I want to make sure I am not missing any potential legal issue that could arise if I bring up needing to go through the step of adding her to the lease or not renewing my tenants lease (it is month to month now). I am documenting everything that is happening. It is just my first one, so I've been stressed about it for sure. If there is any advice, I would gladly accept it.