Your child is going to, likely, cross paths with this girl for years and a parent that feels like their kid is being wrongly accused is not an accepting parent of the perceived accuser. If it needs to get to that spot it will likely happen so just be patient.
Make sure at the end of the year to request that they are not in the same class and if they are don’t accept it.
Sometimes you tell your kid to buck up and handle the situation. Sometimes you take control but only you would know exactly what needs to happen. If you are really worried about it tasks an older sibling or neighbor to keep an eye out for them.