Quarter Zip. Sublimated design with club logo and personalisation (optional).
Sizing: Ladies sizing runs smaller so consider going up a size. The measurements in the size charts are taken from the item laid flat (and not taken from the body). Ladies S would fit a 12-14yr old.
Take a quarter zip or sweatshirt the athlete currently wears. Lay it flat and measure arm hole to armhole and consult the chart.