I didn't read all your responses here, but I had 2 thoughts: 1) Do you live in a climate that is either cold or warm AND humid? Environmental mold loves these climates! Your heating and A/C ducts, or your bathrooms could have hidden mold in them or other allergens giving both you and your daughter a rapid heart rate if you are allergic, as rapid heart rate is one sign of allergic reaction.
2) I asked my M.D. about minerals and irregular/rapid heart rate. He said minerals are a number one issue with the heart. Or rather, he said exactly, "The healthy heart is all about minerals." I had an irregular heart beat that responded very quickly, within a few minutes... and I mean 3-4 minutes, when I put one package of Elecrto Mix (by Emergen-C, no not the flavored ones) in a 16.9 oz. water bottle and slowly started sipping on it. Less than one bottle a day helps me. If I get a candida flare-up my heart starts skipping beats and starts up again with a boom. That's my sign I need more electrolytes. I also use an organic raw wheat grass powder I mix in the morning with water, 2 teaspoons CoQ-10 liquid, and magnesium powder.
Maybe you know that when a heart patient is hospitalized they put potassium in the IV. I'm surprised no doctor has mentioned to you about the connection between minerals and normal heart operation. Potassium and Magnesium are especially important for a healthy heart, especially if people are taking supplemental calcium, as they all have a special inter-relationship which gets upset if a person takes a lot of one and not the others. You can google potassium and magnesium and look for lists of deficiency symptoms.