Apparently she was advised to make every effort NOT to cry in front of the media, because the sort of man who enjoyed hurting little children would be turned on by her crying. I have no idea whether this is true, but it was talked about in the early days
However, what she was like away from the media is another matter.
And you have inadvertently knocked down one of the key tenets of the theory they could not be involved. The idea that they couldn't hide or mask their feelings if they were involved is rather shot down in flames as we know that they were told to mask their real feelings to the media and they could indeed do it.
What you are syaing fits in with my own belief that there is primary source evidence that when required or considered to be necessary the parents, particularly Kate McCann, are extremely skilled at masking their real feelings very successfully even when under enormous emotional and other stress.
Indeed even Menezez seems to have been taken in by it stating in the final report:
"the normal behaviour that they adopted until the disappearance and afterwards, as can be amply concluded from the witness statements."
Oprah transcript:
'Four days after Madeleine's disappearance, the McCanns held another press conference pleading for their daughter's safe return. Kate remained calm as she spoke, but the tabloids would use her appearance against her, saying her lack of emotion implied guilt. "I'd spent 72 hours crying, and you suddenly almost feel a little bit numb," Kate says. She'd also spoken with a behavioural expert who'd given specific advice on how to act at the press conference, Kate says. "They said, 'It's quite important that you don't show any emotion, because the abductor could get some kind of adverse kick out of it,'" she says. "When you get the feeling that if you do [something] it could be detrimental in some way to your daughter, there's a huge pressure on you to do well."
Though it may have done more harm than good, Kate says she doesn't regret taking the behavioural expert's advice. "It was advice given with the best intention," she says.'
And from Madeleine, page 112:
'In fact I would soon be advised by British police experts to try and stay as calm as possible and not to show any emotion in public, so it was probably no bad thing that my feelings seemed to be temporarily on holiday that day. The thinking behind this advice was that Madeleine's abductor might get some kind of perverted kick pout of my distress and perhaps change his behaviour in some way.'
She adds: 'Of course we were terrified by the implications of this theory. It meant that quite natural actions or expressions of emotion caught on camera could potentially jeopardise Madeleine's safety.'