Hi there,
I support Divvy's suggestion that you seek urgent legal advice from a solicitor practising in family law.
You will be advised by your solicitor that such matters vary from child to child depending on a variety of factors. There is no hard and fast rule.
The lawyer will give you advice about your legal options which may include but may bot be limited to court action, and/or family relationship counselling.
The staff at the Family Court are unfortunately not able to give people in your position legal advice.
In the meantime, have you considered the possibility of therapeutic assistance for your daughter such as counselling just for her to assist with her distress - perhaps you could secure a referral to a school counsellor and/or counsellor from your GP?
You may be then presented with an opportunity to discuss the outcome of such counselling with your ex (after receiving advice from the counsellor on how to approach the matter to cause minimal distress to all concerned).
Good luck.