Hi, My Daughter Aged Worms Realised When We Were Talking

Hi, my daughter aged worms realised when we were talking about threadworms that she has them. She didn't know that's what it was so hadn't told anyone so she could have had them for some time. We all took a tablet (Ovex) at 1pm. My daughter started to feel dizzy at about 4pm then got a headache. She was very sick at 7pm. Does this mean the medicine will now be ineffective? What can we do now because it appears she had an adverse reaction to Opex?