Freelance Editing + non competition agreement

I am a freelance editor. Recently a producer (and friend) hired me to edit an hour long documentary for PBS. She was hired by PBS to be the director of editing and I the editor. Towards the middle to end of the project, the PBS executive producer felt that it was necessary to communicate directly with me so that her ideas would only be interpreted by one person (me) instead of a middle-man (my friend + producer). (It's like playing that telephone game when your a kid... ideas get distorted when you have to go through people to get to the end result)

The exec producer of PBS has never worked with freelancers before, but due to severe budget cuts, she hired my boss to oversee the editing; my boss hired me to do the actual editing. The exec. producer of PBS was not aware of what a pain it would be to have to go through a middle man to communicate her ideas.

With all that being said, the doc is finished. The executive producer of PBS called me last minute to edit a short 4 minute piece that is due in three days. Small project, very little money involved. I agreed. I didn't ask my producer if she'd mind. I didn't think of it. I did not sign any anti-competition with my producer, but when she got word that I was working for PBS on this 4 minute project, she became upset and confronted me and the exec. producer of PBS. She told me that from now on I must sign a non-competition agreement.

My issue is ..... I do not work full time for this woman, maybe I edit 1 or 2 projects a year from her (all low pay). She cannot guarantee me a certain number of hours or wage. PBS said they want to continue working with me. They do not want to work with my boss because she does not actually do any editing and going through her is a waste of time and money.

I asked my boss if I went directly to PBS and applied for an editing job, would that non-competition clause apply. I didn't get an answer. Do you think it's fair to sign this agreement? I do not mind signing an agreement that I will never seek employment from any client of hers, but if they actively seek me out, what should I do?