It`s hard to say what the minumum is. Some of it depends on draw length. Those bow weights may be
if the bow is drawn to 28 inches. It`s unlikely that your twelve yr old draws twenty eight inches.
Last October my boy, who is twelve, killed his first traditional deer using a recurve made in the seventies, and he was pulling 39 lbs at his draw length. His arrow was a carbon shaft, with Tusker Concord broadhead(two edge). Total weight of just over 400 grains.
I was VERY concerned about this being enough medicine for deer. He made a textbook shot, slightly quartering away, taking out both lungs. The arrow did not pass thru, but the broadhead made it out the other side. Short, easy to follow blood trail. My fears were unfounded.
I have no idea of how fast his arrows were, I made my decision of allowing him to hunt with a recurve, by the impact his arrows seemed to have on a 3-d deer target. They hit with a good whallop. He killed a deer the year before using a compound bow that pulled forty pounds. That shot produced very similar penetration.
If your girl can get 35 pounds, and the arrows seem to hit hard, she should be good to go.
If I was eight yrs old, I would love to tag along.
Take them hunting, WE need them.
I`m sure good hunting ethics will come automatically from you.