anxiety dog walking

I have a 7 year old beagle Shar Pei mix I adopted a few years ago. She came from a hoarding situation with like 20 other dogs, she was the smallest. She was scared of everyone and everything. I don't think she had ever really been outside much. I did take her to a behaviorist when I first got her and that helped a lot. She has made huge strides over the last couple of years, but she is still really nervous on walks when there are other people and dogs around. She freezes until she feels the "threat" has passed. I have tried to distract her with treats, praise, etc. but nothing works with her. She will not eat treats outside her home, no matter what they are, and believe me I have tried every kind of food you can imagine. She enjoys her walks when she doesn't encounter others, which is fine in the colder months because not as many people are out. It is summer however, and I really want her to still enjoy her walks. Any suggestions?