Marrieeliz In your original post, you said that the tenant was not occupying the property for nine months? This is against her tenancy agreement, she is not allowed to leave it for so long. Also, I would have thought that she would have had to get permission to have jobs done to the property, I know I have to to mine. If it is possible, look on the housing association she is with, their website and see if it says anything or ring them up on another number and enquire if, as a tenant, you would have to get permission to do jobs and how long you can be away from your property, pretending you are interested in renting from them.
Keep a diary of everything they do. I had this in my last home but unfortunately I ended up moving house to get away from the person who was making my life hell. Install the CCTV so that you have evidence but it can't be pointed at anyone else's property, only your own. Take photos of any more stuff left in the entry and put the date on the camera. Voice record any conversations.
Then change your name on her to Miss Marple. 
Good luck, some people need a kick up the jacksy to be normal human beings.