How Do You Know When You're Done? Tips to Evaluate Whether Your Manuscript Is Really Ready

One of my private clients has been working on her memoir for quite a few years.  She's workshopped it through my online classes and with writing partners, and in our coaching sessions, we analyzed the structure and she made many great revisions.  She sent it to a few other writers for feedback and got ideas on what else needed tweaking. 

This week, she emailed me with the big question:  Are we there yet? 

How does a writer know when the book is cooked, ready to send out to agents?