Dog Aggression Training PLEASE HELP?

I have a 5 year old flat coated retriever (Harley). She is very well behaved around us, and other people, knows lots of tricks, and, for the most part, listens well. She's been an angel her whole life and (even though she didn't have much interaction with other dogs) had a few canine friends. In the past few months, however, I have noticed disturbing changes. She is still an angel around us and our friends and doesn't care is we're near her food when she eats (unless its our cats cause they try to eat her food) or anything like that. Lately she has been attacking other dogs. At first we assumed it was territorial; another dog came in our yard so she fought it, understandable. Then she saw the neighbors dog across the street and ran into their yard to attack it, which was when we realized there was a problem. The worst thing was today. My 15 month old cousin was over (Emily). Harley has never had interaction with small children much less babies (I'm the youngest and I was 12 when we got Harley as a 3 month old puppy) but we figured she'd bark and then get over it. We gave Harley a rawhide after some initial barking to keep her quiet so she wouldn't scare the baby, Harley seemed to relax so we let her be and figured it was fine. Emily followed Harley all around the house and Harley started giving slight growls at her (that should've been a warning). We ended up bringing Emily to a different room so she wouldn't bother the dog. A little while later Emily was walking in the kitchen and Harley came out of the adjacent room and baked feroicously in Emily's face and looked like she was gonna bite her. Emily started crying of course and was picked up and Harley was instantly told she was a bad dog and crated and since she kept barking and scaring Emily she was moved outside. I have to say, I think the reson Harley did that to Emily was because she didn't know what Emily was and viewed her more as an intruder or something cause she always fine with new people, but Emily is so little and Harley has never seen anthying like her. I also think Harley's attacts are fear related because she did have a bad experience with dogs attacting HER (nothing serious requiring a vet or anthying but I'm sure it was still traumatic to Harley). Also, she has always been afarid of other dogs in the neighborhood (there are lots) which meant she couldn't be taken on walks till after her first birthday because it took so long to break her of that fear. She still does get a little nervous on walks when she sees other dogs but not near everytime and nothing like before. I thought we had kinda broken her of that fear but I guess not cause it looks like now shes expressing it aggressively. What I need help with now is training her to stop acting like she did today, she is my angel and I expect her to behave as such. I need to know how to teach her to respect other dogs and certainly babies. PLLLEEEEEEEEAAAAASE help. thanks =] oh and sorry I wrote so much I felt it was necessary to explain the whole situation.