Is she in Afib? This is where the top of the heart will skip around while the bottom will keep normal pace. It would feel like heart heart is fluttering or at times skipping. I had Afib and my heart rate was around 130 all the time. When working out I would get to around 160. If it wasn't for the lower part of the heart keeping normal pace it would blow up.. lol At least that is what my cardiologist explained to me.