Should I tell a senior collaborator how disappointed I am? I was part of a small group preparing an overview paper for a special issue, and we missed a final deadline.  All except one of us completed our assigned tasks; the last person had not touched her files for months and was frequently unresponsive with no explanation. To complicate matters, she is a senior member of the community; I'm a mere postdoc, and other members are somewhere in between.

I'm confident I did everything I could to see this paper completed on time, as well as the rest of the cooperative group members.  I've mostly accepted the pending consequences with the journal and my reputation.  I'm also determined to not work with this senior member again.  But should I express my disappointment with her directly, or just cut my losses and move on?
From your description ("final deadline") it sounds as though there is no way to fix the situation with the paper. Moreover, you say have decided not to work with this person again (which seems reasonable). 

So there is most likely no benefit to be had from expressing your disappointment directly. Frustrating as it may be, cutting your losses and moving on is the better option.