"where would be a good place to cut right above the third set of branches"

Yes, I would cut right above the 3rd set and those will be your main colas. You can try to root the cutting. Do a little research on "cloning cannabis". I read that most people have better results with gel over powder for a rooting hormone. Keep them warm and moist and have a little patience. Hopefully it will be a girl and you will be set for your next grow. That's cool that your mom lets you grow. :thumbsup:

By the way, if your plant turns out male, you're screwed and have to start over. You should have started with more than one to ensure one female. Good Luck with that.