fearful dog just began fear biting

Question
We have a beagle we rescued at almost five months of age. At that time she was suffering from separation anxiety, and was fearful of small children, men etc. She did well in obedience school but has recently - today began- acting aggressively while on walks - and bit a boy as he walked by her. I think she didn't see him until he was right next to her. but still very unpredictable and scary for all. Is there anything that we can do?

Answer
If you cannot trust her to behave, then the best thing might be to acclimate her to wearing a muzzle in public.  If you've never done it before, you'll find instructions here:
http://www.morrco.com/trdogtowemu.html
It's not easy to own an unpredictable dog, but it sounds like you love her and want to keep her, so you must protect her against having any more bite incidents that could prompt your local authorities to act.
You certainly could engage the services of a behaviorist to help you condition her to be less apt to take matters into her own paws, but the best way to protect the public is to protect your dog.  You can find a local behaviorist at the IAABC or Animal Behavior Society websites.
Good luck.