Hi,
I dont fully understand what exactly you are worried about but anyway hope I can help a little. At 2 she must be drinking cows milk at home right? So just continue the same here in India - depending on which state you live in there are state co-operative societies (its Aavin in TN, Vijaya I think in AP etc,) which produce milk in sachets or there are private milk producers as well (Arogya in TN). She can drink whatever your parents buy at home. As for avoiding sickness - the usual common sense rules apply - boil water, no juice/ice/water/food from roadside places, avoid raw food outside and make sure she washes her hands well before she eats. In spite of all this kids will fall sick and that will happen whether it is the UK or India. Dont worry too much - she will be ok after the first few days.
Vanathi.