I haven't done any of those, but I've been looking at doing WWOOF this summer too. I know that Helpx is also a good program with a broader range of work options which you could look into (if farming isn't your thing).

If it's your first time travelling, (based of just getting your passport), I'd recommend you stick with Europe, Australia / NZ, or the US / Canada, depending on where you live right now. Those are arguably the safest places for a young, white female to travel by herself. Granted, I wouldn't really recommend your first international travel experience be solo, but who am I to stop you? These programs could give you a solid base for meeting fellow shoestring budget travelers and making new friends.