claig yes, I believe that if she hadn't put 'innocent face' then her question would have been open to interpretation. A genuine question about the activity on twitter; A genuine question about Lord McAlpine, etc.
It could be argued that if she wanted to know why he was trending she could have looked at the tweets, but we all know from threads on MN that people often ask 'what's the deal with x' when the information is freely available on the internet, but they just can't be bothered to hunt it down and instead want a summary.
The 'innocent face' element turned it into a bit of a rhetorical question. Instead of asking a question, it was making a statement, even if the statement was an implied one. Or at least, that was the conclusion of the judge - for a statement to be libelous there must be a statement. It was 'innocent face' that turned the question into a statement.