Yes I agree with you. I think the police might have made a crucial mistake early on. I'm also wondering about the second witness, again someone who apparently knows Nicola, who saw her at 9.10. Saw her on the far side of the upper field, although I read this person only saw her from a distance. I think this witness was a man, from what I've read.
I'm sure the woman who found the phone and dog said she came across a man, asked him about the phone/dog and then he carried on his way towards Rowanwater. Is this the same man as the second witness? She was spotted fairly close to Rowanwater at 9.10. Surely he should come under a little suspicion, simply for being a man that knew Nicola and is looking like he was the last person to see her, if indeed it was her, as it was at a distance. I will never believe she is in the water until she's found in it and even then, it's possible she's been put in there later on now the public knows that the police think she has been in there all along.