This may not help much in this case, but I do know that sodium competes with potassium in the kidney tubules, so if she likes bananas and other potassium rich foods, or she is getting medication with potassium in it, I wonder if perhaps this could be a reason? Its a bit of a long shot though.
It sounds like she's not getting enough sodium in her diet. <br />
If she's drinking lots of fluids then she might be flushing out too much sodium & more. <br />
I've had trouble keeping my sodium level too the last several years, resulting in ileus & doing things I had no memory of the next day. Adding extra salt to food wasn't enough & after my third hospital stay I began taking at least two grams of salt pills daily + salt on food. That's seems to be working well enough for over three years now. The bad part now is that my bp is high. <br />
If she's taking HYDROCHLOROTHIAZIDE for high blood pressure that could reduce her sodium level & explain her ******* ( http://blood-pressure.emedtv.com/hydrochlorothiazide/side-effects-of-hydrochlorothiazide.html )
yes too much potassium gets rid of sodium in the body. I think the doc needs to look at that. She may need a pacemaker if the bp is too low.