There was no reason at all for Kate McCann to have to go and do a 10pm check, because she knew that Gerry left the tapas bar at 9.30pm and hadn't come back. She must have been wondering what was keeping her husband so long?
On top of this, she must have noticed that Oldfield, O'Brien and Tanner, had all left the tapas bar in the wake of Gerry McCanns 9.30pm departure..
She went to her apartment at about 10pm not to check on the children, but to try and find out what was going on? When she got there Gerry wasn't there, neither was Oldfield, or O'Brien. If Maddie had already been dead before the McCanns went out to the tapas bar restaurant, she would have wanted to see if her daughter's body was still where it had been hidden? When she arrived at the apartment I believe that Jane Tanner was there. As soon as she realised that Maddie's body was no longer present inside apartment 5A, she went back to the tapas bar and told those who were present, 'they've taken her, they've taken her, Maddie is gone'...
Seems almost certain to me that the people she was referring to who had taken Maddie, were (1) her husband Gerry, (2) Russell O'Brien, and or (3) Mathew Oldfield..