The only part of this which means anything is everything before “and finds herself,” but all that is too wordy. And while it might sound like it makes sense to describe the detective as inexperienced, if she hasn’t been a detective very long, it’s actually impossible, because she would never make detective without a great deal of experience to qualify her. That title may be new to her, but she ain’t new to the job. So you could make it clear some other way, like so:

A young homicide detective becomes obsessed with her first case when it proves similar to her mother’s murder twenty years earlier.

That’s all we need to know to be interested in reading more about the story and this character. But whatever you choose to say about it, say it in the shortest way possible.