I would not recommend the shot for a teenager. I had it just once in my 20’s and it turned me into a permanently PMS-ing monster, and once it’s in you’re stuck with the effects for however long it lasts (iirc it was 3 months?). It was absolute hell on earth, and i find that even some BC pills (progesterone heavy ones usually, which would make sense given that the shot is progesterone) have the same effects. Pills are a lot of trial and error to find one you like but are the easiest option. I would absolutely NOT let my 15 year old get an IUD just because insertion is usually really painful (i was given a pessary to “soften” my cervix and slightly dilate it before they put mine in and it still hurt so much i was screaming), and honestly that’s pretty traumatic for someone so young. The ring might be a nice idea, i don’t know a lot about that one though.