Evicting a tenant on section 8

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I have a difficult tenant in my property. She now owes me more that £9000 in rent. First, I served her an eviction notice on section 21 in july 2012. As she is on housing benefit, with the advice of her housing officer she challenged my notice saying that her tenancy started on the 12th and needed to have ended on the 11th of the month as opposed on the 16th that I have written. For this, the court ruled in her favour. I then served her section 8 and we are due in court next week. She informed me that her housing officer has asked her to challenge me in court because without the eviction order she would not be rehoused. I went to the house yesterday, I noticed that she had fixed locks into two rooms. When I asked her about it she said she was just helping her church members to stay for some times in the house. Can people please advice me on what to do. Thank you.