We have an 8-month-old yellow lab. She was surrendered by her previous owner. We have had her for about 3.5 months. We hired a trainer to come to our house. She taught my sons how to play with her. We also work with her daily. The problem is that she doesn't seem to like us. On more than one occasion she has bitten my sons and me to the point of breaking the skin. Most recently my son was playing with her and she lunged for the toy biting my 9 yr old. She left a deep puncture wound, my son was crying really hard. She showed zero concern, she just walked away. When they were playing she wasn't worked up or overly excited. She also is not excited to see us after picking her up from daycare or coming home. Is this concerning?