Convincing client to use WordPress

This may not be appropriate for this forum but here goes. I have a client who wants to build a new multi-user site and is concerned that WordPress will not meet her needs. This is for a mid-sized non-profit that wants to have calendars, blogs, Google maps mashups, and eventually 50+ users. It is not a highly challenging site yet the teams seems to have a bias against WordPress. Can anyone give me reasons why someone would choose another CMS platform over WordPress? Thanks!!