How is she making her homeless if she’s giving her plenty of time to make new living arrangements? 

It’s not uncommon for single parents to expect someone in their family to fill the role of a spouse in their household. A single dad might treat his sister like a surrogate mother figure, expecting her to do child-rearing for the child that he had with a woman who is no longer in the picture. Not only is this borderline creepy, but it’s unsustainable in the long term unless the sibling explicitly states that they are willing and eager to take on a parental role in their nibling’s life. The older sister in this story does not want to be a second mother to her niece, and it’s difficult for her younger sister to accept that reality.