This woman wasn’t ready to be a responsible dog owner, but got a puppy anyway, dumping the pet on her sister whenever it suited her travel plans.
Her sister was willing to dogsit on occasion, but that didn’t mean that she could just drop her dog at her house whenever she felt like it. Although it’s nice for pet owners to feel like there’s a backup option for their pet when they need it, taking advantage of a family member and expecting them to shoulder the responsibility of pet ownership alongside them is totally entitled and should be met with some serious boundaries.