My neighbor did this.. What should I say to her about it??

To make a long story shorter, my cousin was here watching my sisters, my stepmom and her sister left, therefore the cars were gone and the front door was open.... okay.. so.. my neighbor (nosy neighbor) comes over, walks in my house, sees my cousin sitting on the computer in the little room when you first come in, walks by him, into my room, and takes my little sister and my puppy and decides to take them over to her house without even asking my cousin (i wasn't home, i left my sister in charge of watching the puppy) my cousin didn't even say anything to her!!!! but he was really annoyed!!!! he thought i told her to go get my puppy and my sister or something.. what should i say to this neighbor?? i also think she has been abusing my dog when she watches her or like today when she brought her back because my puppy is getting aggressive and has fleas now and is sick.. she's been vomiting and has a fever.. what can i do about this menacing neighbor!?! also i saw her push my dog once.. but