Reclaiming rent & other costs after eviction?

Rent Arrears

I've finally managed to evict my housing benefit tenant last week after serving notice in May (I'm in Wales). I used an agent who served a Section 21 because I wanted rid of her ASAP.

The tenant never topped up the rent, most of which was paid by the Council. The amount she was supposed to pay was £100 per month. Rent was only £400 a month in total. By the time she moved out she owed £5400 in rent.
Including court costs, house clearance charges and other fees there's another 1k on top. She was supposed to pay court costs when she got the possession order but obviously she has paid me zilch.

She also stole the key to the oil tank, door key and the wifi oil boiler thermostat. I've managed to get the keys back as I found out where she lives. She claims the thermostat is somewhere in her new council bungalow so I said I'd call again in a month when she's sorted out the mess.

She's the fifth tenant in the house and the only one who has owed me so much. She's also ruined my house with black mould everywhere due to a total lack of ventilation and hoarding crap in every room 😡. Is it worth taking her to the small claims court to reclaim my expenses and/or rent? She gets every benefit going because she's massively obese and virtually housebound but I suppose she'd plead poverty and the court would be on her side 🙄.

Any experiences/comments welcome.