As a Guardian of a "rescue" dog w/fear aggression towards dogs while on leash, I recommend a couple books which has helped me:
"Click to Calm" Healing the Aggressive Dog. Author: Emma Parsons
Or another book: "Bringing Light to Shadow"From Aggressive Rescue Dog to Canine Good Citizen. Author: Pamela Dennison.

You are not alone---many of us have had to deal with the same issues w/rescue & shelter dogs. 'Hang in there. It is fixable w/compassion and patience and two excellent books.


Jasmine's mom.