Hello! Could you please tell me something? My daughter has a bluish ti…

Hello! Could you please tell me something? My daughter has a bluish tint on her forehead when she strains too much. What could it be and what doctor should I consult? It used to be less frequent. A month ago we had a routine ultrasound of all organs, everything was fine. I'm very worried, and my husband says it's veins, blood vessels, etc., it will pass. The sons didn't have this.