What Causes Urticaria After Vaccination For Chickenpox?

my 2year daughter had taken chickenpox vaccine on 2nd of this month.After about two days she developed urticaria.we consult our paediatrician,dermatologists on the same day.Both the docs told its not of vaccination,but may of some other reason.On the seventh day rashes icreases and reduced to minimum after 10 or 11 days.but it is still there.On 12th day we consult another dermatologist,he told it is defenitily of vaccination it will take 3 weeks to subside.Can I confirm it?