Is the FL actually barren or is she just saying that to push ML away?

no one know, in her last life she didn't beared any child, maybe she was living with so much stressed, or her body weakened in her bullied time, or some one did something that make her barren. Her last life was filled with malicious words and assaults so FL might believe that she is like that. But with no proof, I don't think FL is unable to have children.