Why does Mrs. Linde agree to marry Krogstad?

Mrs. Linde and Krogstad were once in love. Mrs. Linde had a sick mother and small brothers to care for so she needed a man with financial stability. This broke Krogstad's heart. Now a widow, the two meet again and reconcile their past. Their relationship is based on respect, as opposed to Nora and Torvald's relationship, so they decide to get married.