<human>: My boyfriend's grandparents passed away, the grandmother 5 years ago and the grandfather last year. They had a lab mix, now 9 years old, and my boyfriend and I decided to take her in because we just bought a house. She has never been around other dogs, but is excellent with cats. One of the reason none of the aunts took her is because they all have dogs and Brandi (our dog) has shown aggression toward them.

My older sister has a 4-month-old pit. She is *very* sweet, and incredibly well trained. When they come over, the two dogs can usually play in the backyard without problems. They have played together 3 times and taken a walk together fine (We've only had Brandi a month). The problem occurred the first time when Canella (the pit) attempted to take a drink from Brandi's water dish. Brandi lunged and bit Canella, but it was stopped quickly and no skin was broken. Both dogs played fine after the incident. The second time, on the 4th, Brandi was laying in the middle of our hallway between the kitchen and the living room. Canella was attempting to walk past her into the living room when Brandi jumped up and bit her. It took a moment more to react and Canella had a small wound near her eye. My sister's girlfriend left with Canella soon after.

My sister, her girlfriend, and Canella are all about to move in with us (1 week). Is there anything I can do to teach my old dog not to react violently when something displeases her?

Can you summarize the given text in a few sentences?
<bot>: My 9-year-old lab mix is showing aggression occasionally with our soon to be housemate's dog. How can I train this out of her?