Lisa Walton bought Pirums Figaro from Shan Allman, of Colwinston, Vale of Glamorgan, for £18,000 in May 2011.
But afterwards she said the animal was "dangerous" and wanted her money back.
After unsuccessfully suing Mrs Allman, the High Court ordered Mrs Walton, of Doncaster, to pay the former owner's "substantial" legal bill.
Mrs Allman refused to take the pony back or return the cash, saying she had honestly described the pony's character before selling him.
She said he never displayed any "vicious behaviour" while her own young daughter, Bethan, was looking after him.
Mr Justice Snowden's ruling means Mrs Walton's farm has been effectively mortgaged to Mrs Allman who can, if she wishes, seek an order for the property's sale.
He added Mrs Allman had "already incurred very substantial costs" but "Mr and Mrs Walton had not made any effort" to pay them.
After the hearing, Mrs Allman, who released footage of her daughter Bethan riding Figaro, told BBC Wales: "The original case that she brought against me concerning the sale of the horse was absolute nonsense and should never have gone to court in the first place.
"I made a number of offers that she turned down which I think she is probably regretting now.
"I'm absolutely relieved that the case has come to an end and I've got security against my legal bills."
A horsewoman locked in a four-year legal battle over a pony she claimed was a "raving lunatic" must pay costs of £140,000.