Diane Hampton is quite right in stating that it is wrong to stop Bethany Ogley visiting her sister’s grave in school uniform.
Her other point about the colour of Bethany’s hair is wrong. There is no reason why teachers should not have their hair coloured, they do not have to conform to a uniform code. It is wrong, however, if one child is being penalised for having coloured hair when others are getting away with it.
Obviously the dress code needs to be clarified and upheld fairly for every pupil.
If Bethany’s mother doesn’t agree once this has been done, then I assume she is within her rights to find another school for her daughter, but she should bear in mind that no-one likes a troublemaker!