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http://www.petrescuebyjudy.com/ I live in Altamonte and know people that found their rescues through her. They even have a section for Senior dogs. Can't hurt to gve her a call. I feel so bad for you. Nothing is scarier than another dog, no matter how nice in normal situations, goes after your beloved #1 dog. It sounds like you have done everything. This guy is in Seminole County and I've talked to some people that he helped. Couldn't hurt to call him but I'm not sure this is something that can be resolved.
http://www.pawfectiondogtraining.com/Good luck and keep us posted! Also I know whatever you do your brother will understand. I'm sure he just wanted his Daisy happy if it's with you or with another family.