The group looked at return of menses as a marker of physical health in anorexia nervosa in 225 patients in their FBT program. On average patients needed to get to 95% expected body weight before menstruation resumed. Interestingly this is almost exactly the same number as indicated by pelvic ultrasound to demonstrate that ovarian and uterine maturity in adolescent AN occur at 96.5% EBW which was found by Brian Lask's group (Brian being somewhat critical of a reliance on resumption of menses as a marker of health - preferring data from pelvic ultrasound.
The group also note that "individual differences in weight trajectories should be taken into account, as many patients may have higher individual “setpoint” weights than the average EBW calculations provide. These discrepancies, however, may also be related to weight maintenance necessary to restore menstrual function in adolescent AN as some patients will only resume menses at weights >2 kg’s above the level that supported menses prior to the onset of amenorrhea". SOme patients will lose menstruation at higher body weights than others and are likely to need to get back to higher weights to resume menstruation. All of which means don.t rely on any number on a chart to work out what weight is the right weight. Use your experience of your child when she was healthy (I can safely say she here), think about when periods were lost (and maybe go up 2 kilograms).
Of course target weight should be thought about in terms of ranges and are moving targets as we are expecting growth in many cases.
ROM occurred after an average of 13 sessions of FBT (although there was a large standard deviation). What I read from that is that there is a need to push very hard for weight gain to 95-100% of weight in as few sessions as possible in FBT to ensure a rapid return to physical health.