My five year old sister refuses to use the toilet when she needs to, she is the only child my mother has had trouble with in this regard out of four.
A couple years ago she was beginning to use the toilet as you would expect, she now claims to be afraid of using the toilet for some unknown reason. (Which probably means I should have asked this sooner)
The promise of rewards if she uses the toilet doesn't work, nor do threats of punishment.
She will not tell us when she needs to go to the bathroom despite our attempts to encourage her to do so.
This is quite frustrating, a bit of advice would certainly help.