My 12 year old daughter with Autism was just put on 1mg intuniv she has normal bp. How much will this dose lower her bp.

Not much if at all. or healthy children, such a low dose of Intuniv should not have any effect on blood pressure.
Perhaps no change. There may be no change in blood pressure in your daughter. Only 6% of patients taking this medicine experience a lower blood pressure, and in those cases, perhaps a change of 10% is common.