Most places don't have them in CA anymore because of water usage.  

I don't really have a problem with it but I I will need to renegotiate the rent with her for the extra person and water usage and wondering how to come up with a fair amount for that. 

In either case if you have proof that the tenant was still there during the time of usage it's between the tenant and the utility.

I charge $25 per pet per month.  4 animals is $100/m additional rent to you which helps you pay for the added usage of the property. 

Also, they plan to use the basement as an additional bedroom and you are aware of this planned usage.

For any dirt or damage beyond what would happen by normal usage, then tell the tenant they need to clean or fix it - or it will come out of their security deposit and put that in writing.But, be sure of your local laws, in case you have to give your tenant written notice of their rights, etc., like in CA.

It's inappropriate for the buyer to have any contact with the tenants until after closing.

Since a backlash on Facebook and Yelp, the addendum has been withdrawn and City Park Apartments has apologised.Passing the move off as one to help residents, a statement from community manager Ana Raphael in a statement read: "As part of opening its pool and an anticipated pool party, City Park desired to provide some protection to its residents and its owners from usage of photos on its Facebook page from all community events, including the opening pool party."

I found out from the condo association office that the police has been out to the unit a few times on drug usage and charges have been filed.

If so, and if it shows a clear rise in power usage over the prior year when compared to the current bill, then I'd draft a letter or email to inquire with the tenants as to if they are aware of any possible cause of the power usage increase.