Well...I got heartburn a few times on the Master-Cleanse and I just mixed 1 tsp of baking soda with 1/3 cup of water and drank it back. Stand or sit (but don't lie down) after drinking it down and you'll feel lots of burps come up. (very satisfying!) Then...within minutes the heartburn is gone. Works for me every time.
Also you can tell her to drink more water in between lemonades.
*tip* some people get sensitive teeth while on the Master-Cleanse - it's adviseable to make some baking soda water and rinse your mouth out with it a few times during the day. This alkalizes your mouth and can save people from that sensitive tooth thing that sometimes happens while MCing...