SFWG Study Hall

My first question is why was her powers and soul put in the ruby, but that wasn't the question. The second question is how much control does this ruby have over her? What you need to figure out is what kind of story you want to tell "revenge" (go after the wizard for killing the witch), "under dog"(powerless fairy goes after wizard for stealing her ruby)or "lady in distress" (fairy is powerless and is waiting for prince "charming").
The first two would lead into some type of pursuit, most likely she would try to employ some type of help or go directly after the wizard and fail, at least on the first go. The third line would require setting up another character that would have motive to save her, like an other fairy, maybe the humans that though her out in the first place, a boy friend, whatever.
Now seeing that you already set the story in the fearies POV,if you do choose to have her traped by the warlock, you may want to consider trying to excape the warlocks cluches, while she needs to get the ruby back. Maybe there are other people the warlock captured and she bands with them to plain an escape. Maybe the warlock, captures her and her ruby when she run in tears from the witch hut or maybe...