Questions I would have asked:
1. Why have you not released the CCTV you have of Nicola? Or can you just confirm for the record that - aside from her own Ring doorbell footage - there is no CCTV of NB on the morning she disappeared?
2. You said there is no evidence of third party involvement or criminality. There is also no evidence of her entering the river, correct? Just to clarify then, what specifically has caused you to speculate that it is more likely she is in the river than chose to leave the area for any number of reasons?
3. I understand that you would not want to reveal specific personal vulnerabilities, but why did you leave it 3 weeks to reveal that NB was high-risk? Wouldn't have doing so increased useful public involvement in those critical early days whilst dampening unhelpful speculuation? Do you regret not releasing this information sooner?
1- why do they need to release all the cctv of her? What does it add if she's seen walking past a neighbours address or driving? What does it add? She was seen and spoken to at school and in the field by independent people.
2- the abduction theory would need so many things to go exactly to plan that it just would be so unlikely to happen. How is someone managing to get away with a body and not be seen by others in a reasonably busy area.
She had possessions found next to a river, this is the most likely place she has went. Cctv has shown she didn't leave most of the exits and they've requested dashcam for the others.
To voluntarly make yourself missing requires planning and money. Bank accounts will be checked to see if she was doing anything prior to going - withdrawing money, moving money elsewhere. Her face is out there and someone would have recognised her by now.
Providing exact reasons why they think she went in the river could be hurtful for family to see in public. You do not need to know this, the family will have been told but you have no right or need to know this other than to satisfy yourself. May sound harsh but it will not affect your life by knowing or not knowing this other than to satisfy a nosiness.
The simplest solution is usually the correct one. This is not an Agatha Christie novel, or a knives out film (for those much younger)
3- anyone who knows anything about missing persons could tell she was graded high risk given the number of officers involved. The public became involved early (some became far too involved) so no, it wouldn't have made any difference. If the police had given reasons for saying high risk then it's hurtful for her family and friends to have this released, the police will very rarely release anything specific as unfair to the individual (if they are found) and also for family.
The police tried to push the public away from speculation by speaking about her partner not being involved but it still didn't stop, it didn't stop people digging up reviews of the caravan park, or of folk stalking Nicola on Facebook, starva etc. I very much doubt they regret waiting to release this information, probably more likely that they regret that they have had to release it at all as it will be distressing for family and friends. Family will have had the investigation explained to them but they will understandably be hoping that she turns up safe and well.