Bloodborne the little Yharnam Girl, random thoughts

It's a little side mission in the game where the girl's fate is to die either option you choose. Those are Dark Souls games for you. But I had a random thought about her weird sister. If you don't give the little girl her missing mother's brooch and tell her to go to the safe haven, she dies. Then you can receive her ribbon that is really just a cosmetic thing off of a giant pig in the sewer, indicating she was eaten.

Then you have the option later to give the ribbon to her sister at the window but in a matter of a few seconds, she goes from worried about her sister to psycho, indicating she wanted the ribbon all along while laughing sinisterly.

Later she commits suicide and then you get a white ribbon.

But I had a weird thought, if that's indeed her sister why did the little girl say she was all alone? It could be that the sister was evil all along and she felt alone but it's weird how no one was in the house before and all of a sudden there's this sister.

I've also heard the sister changed due to the palemoon and it makes monsters, when the sister killed herself, she must have remembered the girl she cared for.

But it is a story loophole if anything because why would the girl claim she was all alone if she had a sister in the house all along and then who is the mysterious sister?