I don't think luxilon is a good choice for an 11 yo female junior. Hold off on the poly until her game is fully developed. Luxilon is hard on the wrist, elbow and shoulder. Takes power away from the player's shot and is intended to add control and spin for players who can generate power. Also, if you still insist on playing Lux, restring it every 2-3 weeks even if it has not broken. It goes dead and will be even more hard on the body by that time.
I would suggest a good synthetic gut like Gosen, or PrinceSynGutDuraflex until the player is very advanced. Then maybe a good multi like NXT or Technifibre NRG2 or Tecnifibre X1 BiPhase.