You are still confusing the person with the company.
There is no issue here. The lender owns the car. If the company does not pay the lease payments, they will repossess the car. The liquidator probably could choose to continue the payments, but it's unlikely to be worth it.
Your sister has no rights or obligations.
You have to understand the position fully, before you can begin to negotiate. As I already pointed out, the bank will not want the car and so your sister could offer to buy it from them. But, in anticipation of your question, no, they won't lend her the money to buy the car.
Brendan