He certainly is not challenging her for rank. D

You need ot rule out a physical cause really, but...

Am I right in thinking he is around 7 months old? If so, he may be going through the second 'fear stage', which some puppies goes through. If so, he is no doubt weeing on her bed as it smells of her so is familiar and somewhere he feels safe. This would be especially so if he is especially attached to your daughter.

He will probably get over it, if it is that, but watch out for any other signs of distress, just wash the bedding well with biological powder, and the mattress.

You might find a DAP diffuser in the house helps.