She can only take it back IF the contract or agreement of sale specifically provided that she could regain possession if you feel behind on or defaulted on payments. If the agreement did, she can take it back in accordance with the provisions in the contract for default: such provisions or terms are legal and enforceable.But there must be something in the contract giving her this right. Without such a term or provision, she cannot regain the business, but can sue you for the money you owe her but have failed to pay.