She's not charging for it though? As far as I know.
But if someone came along and wrote a great book about the case, I'd gladly pay for it. Woodward & Berstein etc. didn't do it for nothing did they 
Like you I didn't know a great deal about Sonia Poulton so I've been doing a bit of catch up.
To say I am underwhelmed is putting it mildly (I've just slogged through the transcript of an interview she conducted for Icke TV).
I would say if you are waiting for a "great" work which might give some definitive indicators as to what happened to Madeleine McCann ... the promised documentary is not going to be it.
As far as I am concerned the only chance Madeleine and her family have for resolution lies with the current police investigation being conducted by the PJ and the Met ... and we should throw all our weight and good wishes for success behind that.
Just what is the point of this documentary anyway?
The only innovation is going to come from the police investigation not a wannabe.