You should try the calamine lotion
and antihistamine medications. Nothing can be said about whether the lesion is
infective or not without a clinical examination. She could take some oral antihistamine medications for the itching.
If her symptoms persist even after a few days it would be best to consult a skin specialist and rule out any other cause including a bacterial and fungal infection as the cause of her symptoms.
Let us know about how she is doing and what your doctor advises.