Where does she play best? where does she want to play? Start there and work it out. Stupid fast 9 year olds sometimes become average runners at 13, and slow kids become fast. Its not the time to really begin setting her up for her future. But in the spirit of the actual question. If she can handle it, I would put her at Short. Speed helps there and what ever she learns there will help her at any position she plays in the future. I would say more then 50% of all college outfielders played SS in HS, and its likely that 99% of them played SS at one point in their 10U-12U days.