Is what the elder sister did—describing her sister with inaccurate characteristics to prevent her engagement, and directing the suitor to another sister—considered deceit and injustice?

If your sister lied in what she told the man about you, then she is sinful for her lying and deceit. Her justification for what she did—her desire for your older sister to marry—does not make it permissible for her. We advise you to overlook her mistake and not hold it against her, as she may not have had ill intentions, but she erred.