Backstory: My girl just turned 3 and I've had her since she was 8 weeks. I used to take her to the off-leash dog park virtually every day for her first 2 years and she never aggressive, but I had to relocate to Europe for work and have recently returned after being gone 13 months.
While I was away my sister stayed at my house and looked after my girl for me with the help of my parents, but they warned me she has started to become aggressive towards other dogs. I didn't believe them as they used to tell me this when I was in town but I never had any issues with her being aggressive. The last two days I've had her out and as soon as she sees another dog…the ridge on her back is up and she starts snarling and even tried to bite a dog that got close to her.
Based on what I've read this might be related to her taking an alpha role when I'm not around, and since I've been gone for so long shes assumed that role full time.
Not sure what the best way to fix this is? She also has been staying with 2 other incredibly passive dogs (labs) and gets along with them without any problems.
Appreciate any input so I can return to the off-leash parks, thanks!