My Grand Daughter Now 15 Yrs;her Milk Teeth Did Not

my grand daughter now 15 yrs;her milk teeth did not fall as usual even at the age of 7 or 8.at what staage her parents should have started the process of setting right this problem?should it be immediately aftr 7 or 8 year or at what stage of the child life the treatment should have started.now she is 15 years and may be whenshe was 12 or 13 peraps he arents might of woken to the situation now at 15 year she i undegoigtreatment which is causing her unmanageable pain while eating,chewing etc.i have been telling themeven when she was 7 or 8 to do the remedial process;were they negleted her cae or tis treatent could have been done earlier than between 12 and 15 years