Welcome to HCM .
Please wash her eyes with plain water and avoid rubbing them.few drops of piriton
won't cause any harm as such but redness
and dryness of eyes might occur.
Piriton contaIns antihistamine chlorpeniramine which might relieve itching temporarily however unless the cause or allergen for the itching is diagnosed it can't be treated appropriately . It's best to keep your child under supervision , talk to her doctor about any worsening of symptoms or development of new symptoms like rash ,fever etc.
syrup or drops containing hydroxyzine
might be used in prescribed doses as per your doctor to relieve any allergic reaction
Hope that helps you.
Wishing your child good health.