section 21 failed

Possession - Section 8 and Section 21

I have recently had section 21 proceedings thrown out by the court after a hearing as judge declared that two months rent in advance ( i.e. tenant doesn't pay for last month in property) was a deposit in all but name and dismissed my possession proceedings.
The rents rent is up to date but reason for asking her to leave was abusive nature to me and general problems.
The property is a licenced HMO and this causes me problems when letting to other tenants.
Although this was her defence on my proceedings she has not taking action against me for not registering a deposit/ month in advance from start of tenancy in 2006.
I offered her back the disputed amount in 2012 and she returned my cheque.
any advice on if there is anything I can do next or is she now a sitting tenant ?
Any help would be appreciated.
sean