Using the needle as Sebille (she needs to be selected at the time) will bring you into a dialogue, where you can look up her past victims, future hits, etc. At least, it does for me; I couldn't get it to work for a few minutes at first, but I figured it out so quickly I forgot how I did it. Sorry :X
Also, total sidenote: one day, before he could connect, I found out that my friend DCL has the needle on his character's hotbar. Me and my other friend now joke that he does it for the "combat lore", and that it synergizes with Glass Cannon because it means that he can use it 6 times a turn instead of just 4. Great stuff!

Edit: You need to select Sebille as your origin story during Chracter Creation in order to get it.