Maddys vet bill A rehomed x race horse

Maddy has been with me for 4 years and over that time has always suffered on and off lameness and abscesses without any known reason.  However she was brought in last week with lacerations around her hind right hoove. I first thought was she had caught it in the electric fence tape.  I called vets and sent pictures and was told that or looked clean and to continue as I was but any problems to call.  On Monday her leg swelled and again called vet.  They came to see her on Tuesday and immediately said she needed to be hopitilised as xrays needed incase there was any bone damage and told that it would mean PTS.  I took here in waiting patiently today for the call.  Gobsmacked is a understatement.  Yes she will be fine but has to stay in until at least Monday
The xray showed a hairband embedded round her leg. 
I have no explanation as to how it could have possibly be put there or by who.
Her flesh had grown over it. 

Most of my horses and ponies are either rescues or rehomes but netherless my world and nothing would sto me giving them the best I can but would really appreciate any help with this up and coming vet bill.