I remember your gal from local elite school. Suggest you apply IS for now. Not necessarily to wait until p5. Cos the line is very long for most of the schools. Friend’s gal from another elite school applied for y4 at ESF school with siblings but not optimistic even for year 7 entry ( Kowloon and NT side )
For me where is HK side, the line is not long for siblings but long for outsider)