Sisy is an intact female about to be 3 years old. She's always been a very friendly dog with adults, kids and other dogs. I take her out daily for walks around the neighborhood and she meets and greets everyone. Every week or so I take her to the dog park to meet new people and dogs. Never a problem with aggression.
However, about 2 months ago her behavior started to change. She's now standing her ground and growling at dogs and people who approach us (the same people and dogs we see every day). She's charging at joggers and cyclists and has no patience with little noises around the house and starts investigating and growling. I've had a couple of handy men working around the house and she got really upset and I had to put her inside the crate. It looked like she wanted a piece of them.
Has she reached maturity and needs to be retrained? What am I doing wrong? The food is the same, she has no apparent health problems. She's the same sweet dog with my wife and kids.
Thanks for any adivse...