Anyone who believes that in these cases parents are always innocent, may also have a screw loose, and indeed be a little naive. I have no opinion either way as I do not have enough information/knowledge about this to make a solid prediction of the conclusion of the case; but to label those who believe it POSSIBLE she could have done it, as having a screw loose, is IMO a bit cheeky, especially seeing as how you are making an opinion-based judgement by saying that she definitely did not do it.
To the OP: I believe that the formal suspect status is to protect her, and also to help police as they can ask more questions; but it's also now being said that her solicitor has warned her she could be charged soon. On one hand, I don't think they could charge her without substantial evidence (and they have had a while to get evidence together, plus help from British Police). On the other hand, I feel the Portuguese Police are definitely eager to frame someone. With the involvement of the British Police, though, I can't see that they would 'frame' an innocent person unless for good reason (ie, suspicion of guilt). This is why I am unable to make any judgements: we don't know what the police are thinking or what is happening over there right now.
A couple of weeks ago the police asked the McCanns to stay in Portugal and told them it would be worth their while as they were close to concluding the case. They will have known back then who they wanted to frame/had evidence to frame, so it is very clever maipulation that stopped the McCanns going back to the UK.
I think people are just struggling to believe how a doctor (yes, a doctor - someone who is supposed to preserve life and have a caring disposition and desire to heal), who tried so hard to have children, could do this to their child, if she is indeed guilty (which no one knows apart from them and the police).