[chepukha]

Hello,
My 2 year old daughter was diagnosed with tuberculosis. It is only at the beginning. The X-ray photo of her lung shows no serious problem. Doctor told us to let her use isoniazid syrup once a day for 9 months. She just started taking it yesterday (Thursday) but immediately had diarrhea. However, her stools have bright yellow color, and don't smell bad. Even though she had diarrhea 8 times the first day, and 4 times today, she had no diaper rash.(Her skin is very sensitive, and she usually gets diaper rash easily). She is still playing and eating normally. There is no sign of fatigue.
We could not contact our doctor until Monday to ask for advice. Therefore, I made some research online, but I found that diarrhea is not a side effect of isoniazid syrup.
Could somebody please explain me why the medicine causes diarrhea? Is it something very serious? Should we stop giving our daughter the medicine? Should we give her pedialyte? I really need some advice ASAP.
Thanks in advance.
Chepukha