What Causes High Heart Rate Along With Low BP In A Teenager?

My daughter is 14 sick fever 102.4 vomiting took her to ER they gave her 4 liters of fluids, antibioticsm blood work urine. To Make a long story short her heart rates high potassium low Bp was low now stable white blood count high. What has me concerned Is her neutrophil pct is 89.2. Should I. E worried because my research has got me scared to death.