Twflyer

We are planning a move to France from the US. Our 9 year old daughter, now in US 3rd grade, speaks French with fluency (she does need work in reading and writing). My question revolves around when is the better of two possible terms for her to begin in France. Our choices are either the last year of Primary or the first year of secondary. I hear that the transition from the primary to secondary is a tough one for those already in the system. My thought is that either year will be a hard transition into France anyway, so why not have her go straight into secondary, 6eme, and therefore not have back to back years of hardship. Any thoughts on the validity of this plan? Would there be any benefits to start her first year in CM2? Are there any benefits to starting her first in 6eme? thank you, andy