Hugs to your sister, that is horrible!<br><br>
Water can be very hard to keep down with a stomach virus. I'd try a drink with electrolytes in it - you can get them at the health food store, or you can try Vitamin Water or even Gatorade if you can't find anything else. Small sips at a time to fool her body into accepting it.<br><br>
The lack of water might cause a dip in her milk supply, but she should be able to regain that once she can stay hydrated. It might take a few days, but it will come back.<br><br>
She should keep nursing. Her body will take what it needs for the milk, and the antibodies the baby gets from the milk will help prevent him getting infected too.<br><br>
Since she is nursing, she needs to watch out for dehydration. She may need to see a Doc to get some meds to stop her from puking and / or get hydrated with an IV.<br><br>
A lot depends on how long she has been puking for - if it has been just a day, she's probably still OK. If it has been days, then she needs to be careful about dehydration.