Just be thankful they are gone.
It is far worse to have a tenant who cannot pay and who refuses to leave.
Next time, if you rent again, join the NRLA and do it properly. There are a lot of boxes to tick: Right to Rent leaflet, EiCR, energy rating, gas safe, properly held deposit etc. You need to tick each and every one, and be responsive to requests for repairs etc.
You need to see it as a profession.
You have saved a lot of money on letting and management fees. You have not had any voids for 5 years. Treat this as a business cost. Give her her deposit back, be thankful that she has formally said you can dispose of the furniture (otherwise you would have had to store it for 60 days), and inform utility companies that she has gone, with no forwarding address, and that you are taking over from the date she departed.
Then you have your clean break with little more than the loss of three months rent.
And show a little kindness. Things are almost certainly tougher for her than you.