What is the ruling on a girl continuing to postpone her marriage to a suitor who proposed to her, due to her attachment to a relative of hers who married and had children, despite her repeated performance of Istikhara without success?

A girl should not become attached to a non-mahram man. If her attachment to him occurred without her seeking or choosing it, then there is no sin upon her, and she must turn away from him. However, if it was by her seeking and choosing, then it is forbidden, and she must repent from it. If the suitor is a man of good character and religious commitment, she must accept him, and her lack of attraction to him due to her attachment to the non-mahram man is not to be considered.