Abby has attacked lallas last night, it was so sudden! Lalla is okay but she didn't understand why her best friend would attack her? Abby has been a bit grumpy lately but surely she wouldn't attack lallas because of it? Now I am so scared to leave them alone together! They have grown up together, abby is a year old and lallas is 14 months, but abby is much more stocky and stronger than lallas so I'm stressed that she will hurt her. Abby is normally a happy puppy. Has this happened to anyone else and what could I do? Abby has been on heat, she isn't pregnant but her nipples are swollen, so that is also stressing me out, could this be why she is attacking lallas?