In my opinion people have a duty to report an incident which doesn't appear to be quite right to them if it involves a child and in particular if the child who caused the concern resembles a missing child.
People have a duty to report anything they feel is suspicious to the police. That's what this woman did, although I haven't seen it confirmed by the police afaik.
If she was dissatisfied with the reaction of the Spanish police and was really convinced that her sighting was important there were other options. She could have found the number of the PJ in Portugal and told them. She could have contacted Crimestoppers in the UK or Leicester Police.
It seems she did none of those things, she stayed quiet for five years instead. Then she spoke to the media. That wasn't in the line of duty. In fact it was counter-productive if OG had been informed because the story about her sighting was repeated in the Swiss media. The family concerned could have been long-gone by the time OG got round to investigating her story.
It seems the family had nothing to hide and came forward to make that clear. Another sighting explained. Despite the excitement in the media it was just another false alarm. End of story.