Grown sister wants to keep my neighbors lost dog

Sister is 35 years old and lives 30-50 mins from me. She came over Friday night and told me she bought a new dog and wanted to surprise me by not telling me. So this morning I’m leaving the neighborhood which has 5 different ways to leave and had to cut through a different way since maintenance was being done on my normal route. The stop sign has a stolen dog and picture on it the exact same dog. So I called the number and they mentioned they got the woman on security camera but can’t identify her. Met up on the owners lunch break and y’all it’s my sister. My sister is leaving tomorrow and I’m not sure how to get the dog back to owner without setting her off. Obviously just talking is out of the option. She threw an iPad and fork at her boyfriend before just because he thought they should return a pack of sticky notes she bought and wasn’t using. She also reversed the car into a bush on our front lawn, didn’t even stop she just kept trying to go over it and it wouldn’t let her. Not sure what the reason for that one was. Call the cops or have the neighbors come over and handle her?