messaging plugin on an online counselling site

I have been asked add some additional functionality to an online counselling website I have built for a youth charity and wondered if the messaging plugin would be suitable.

I want the young people who sign up for counselling to have access to their private section of the site (I can build this part) but use the messaging plugin for one to one messaging with their counselor.

It need to be secure and the person being counselled should not be aware of any other users. In effect it will be a private email service.

Can messaging help with this, or would I be better looking at a third party solution outside wordpress.

Thank you for your help.

Mark