You have now moved the discussion on from the “couple” question. IMO YM lacks the ability to perceive how her actions may have come across to a couple in their situation. Was she used to dealing with parents whose child had disappeared without trace? Coming on like some interfering busy body member of the public asking personal questions of a couple who had every right to be confused, suspicious and upset, it’s not IMO massively surprising if she got the cold shoulder, but you and she are claiming that it was only to her that Kate confided her fear that a couple had taken Madeleine? Seems highly implausible to me.
Mrs Martin worked in child protection, which can involve familial child abduction and children being taken into care. Both involve dealing with the bereft mother in the aftermath, so she was not walking into an situation which was beyond her experience and capabilities imo.
I can't understand why an offer of help from someone with her qualifications would be rejected by people who were desperately in need of help, information and comfort.