It definitely sounds like this one:

www.dokuga.com/fanfiction/story/11137/1

One Sidedly Yours by Sesshomaru's Secret Admirer Reviews

She was the only one who understood him. She was the only one he allowed to remain by his side. He would forever regret the crime he committed that night which caused the start of a never-ending nightmare for her. He promised no other would hurt her like he had. He would ensure her happiness, even if it meant denying him his own.
Rating: MA - Universe: Alternate - Status: Incomplete - Category: Chapter Stories - Genre: Drama, Romance - Updated: 05-10-20 - Created: 03-22-20 Chapters: 22 - Reviews: 72 - Words: 48,547 - Reads: 36,730

I'm trying to find a story that I want to say I read at the beginning of last year. It was 100% on this website and not another one. Hopefully I'm not getting anything mixed up with the details and if I do, I apologize in advance.

The story takes place in modern times. Kagome is being raised as Sesshomaru's sister. Something happens and he attacks her and leaves her scarred. I want to say she gets with a friend of his that is a cop, but it might not be his friend. She adopts Shippo I believe and that helps to break up her and the cop. It wasn't complete when I read it, but it might be now. Any help would be greatly appreciated!!

That is the story I was looking for. Thank you so much!!