Oh dear, go and see a doctor, and he will prescribe you some stuff before the ecoli takes form. Remember to not drink from her tap again.
And don't think about it, just go and seek medical help.
So this was tap water? How has E-coli got in to the water system?
Presumably if it's in the water system and the water company knows about then it can't be that large a dose can it? Otherwise wouldn't they shut the pipes down?
Just call NHS Direct or the Quack. Bunch of internet pixels probably aren't going to make you feel a whole lot more reassured.
How does she know there is E-Coli present in her water system? If there was anything in the drinking water the local supplier would have cut off supplies to all homes affected. Sounds like a panic for no reason to me.