Will She EVER Reply To Your Submission?

Q. An agent has had my novel manuscript for over four months. Via an e-mail, the agent said my ms had been read and she would get back to me four weeks ago. I've heard nothing more. Is this an unusual length of time or should I not be concerned (as I am)? I am a published author but have only used an agent one other time. This one requested my manuscript after I met with her at a writers' conference.
- Pearl

A. Well first let's address the good things here. You went to a conference and met an agent. Awesome work there. Second, you didn't hear back from the agent about a submission so you followed up via e-mail. Awesome work there, too.
It sounds to me like this agent is just very behind, or possibly just sloooow. If I were you, I would start contacting other agents. If this agent does reply, you're in luck.
As far as the "length of time," - that's tricky. You submitted your work X weeks ago and then followed up. From the follow-up time, I would give her three months at most. After that, assume she doesn't want it and is too busy to reply.