When this woman is concerned with her sister's behavior, she asks Reddit:
My (26f) sister Sasha (31f) and I are very different people. We aren't BFFs but we love each other. Sasha doesn't have any kids and I have 3 (6f, 2.5m, 1.5m).
Sasha got a dog after graduating college. Right off the bat, she treated it more like a human than a dog. She took it on road trips, just the two of them.
Once she even dressed it up for Halloween and took it trick or treating alongside my kids. I worried she was replacing real human interaction with a dog.
She also did some search and rescue with it which maybe gave her a stronger than usual attachment to this dog.
A year ago, Sasha bought a jogging stroller so the dog could still go on walks with her. It was old by this time and had arthritis. Now let me clarify, this was not some cheap bargain basement stroller, this thing was quality.