You don't know who was with EG when PF phoned.
The crying was significant enough for PF to call a local friend late at night to discuss.
Misty PF's wit stat makes clear she knew who the McCanns were as she saw them walking around. Consider the McCanns entering and exiting via the side gate as they did during the day along with the children and PF sat out on her balcony. Yes PF did know the children were left unsupervised in 5A in the unsecured apartment based on the crying which ceased when she heard the patio doors slide open.
Sorry but I disagree almost entirely with all that.
If Mrs Fenn KNEW the children were alone and crying...if Mrs Fenn had experienced a home intrusion days before....why, oh why would she have "phoned a friend", chatted for 75mins & let the crying continue rather than contacting OC reception or the GNR? Did she care so little about what may be unfolding downstairs & so little that the episode didn't warrant mentioning to the parents the following morning?
She could see precious little of 5A sitting on her balcony, let alone the side gate. Furthermore, the sliding of the patio door may have been a babysitter leaving rather than the parents returning - she was indoors & didn't witness anything visually.