There's plenty, plenty of research establishing that fermented foods actually AID digestion and absorption -- stimulating stomach acid and adding beneficial bacteria to the digestive process. In addition, Kombucha is actually a great source of all the B's.
I can't link you to the research about the digestive benefits without looking it up, but you could certainly google it, look it up on pubmed, or get some answers from folks on here. In the meantime, ask her for her source.