My Daughter Is 20. She Gets Dizzy And A Rapid

My daughter is 20. She gets dizzy and a rapid heart rate (around 200) when working out with weights after 20 min. on the elliptical. The dizziness lasts for 30 min. or more after resting and heart rate is still about 120. This didn't always happen. The only thing that is different since this started happening is she now takes the pill. She is on a cardiac event monitor now and for the next 2 weeks. I don't think they are looking at hormones, but could hormones be the cause?