As an installer, do I have an obligation to service complaints if my contract was "to furnish and install" a stairlift?

My company agreed to install a custom stairlift for a DURA client as a favor to her. The City was not willing to pay the other bids. So agreed to install a specific lift to manufacturer's specification. The manufacturer of the lift provides a 3 year warranty on their equipment. We had a factory rep present during the install and they acknowledged the lift was properly installed and in good working order. THe contract with DURA stays our requirement was to "furnish and install" the lift. And the customer was obligated to sign a completion certificate so we could get paid. Even though everything was done properly (According to the manufacturer) she refused to sign and our final payment was dragged out for many weeks, causing us harm, until finally DURA went around her and paid us. THis woman has complained constantly, we have been out, DURA has been out and the factory has inspected multiple times and always stays everything is fine. SHe now continues to make complaints about the equipment (not the install) and DURA is expecting us to send someone out to service. I believe she has breached the agreement, that we did not warranty beyond a proper installation and want to ignore her. Do we have any obligation to continue to provide free service to this woman? I told her she can hire whomever she wants to come service it for her. Please let me know. I am thanking you in advance.