Care package for Ibby, anyone?
OK, so let's think about this. Ruling out hormonal BC, your alternatives are condoms, spermicide, yanking it out at the right time, NFP, and combinations thereof.
NFP = Natural Family Planning. It's got a bad rap, but when it's done right can really work - especially as part of a combo. At your age doing all the complicated temperature charting crap isn't going to be likely, so along with just keeping track of days (and keep in mind, also at this age - or any age - her cycle may not be regular) there is a thing called cervical mucus. Sounds gross, but it's actually a pretty good indicator of when you ought to not be doing nothin' even with a layer of latex.
Check out this link -
http://www.mjbovo.com/Contracept/Instruct-NatCerv.htm