I don’t know, the British are quite picky with their tea, kinda hard to believe she’d turn around on it so quickly, however perhaps the water’s “taste” could be not suitable for British-style tea.
If you’re going “water’s ‘taste’ wtf?” If you’ve traveled to other counties and tried their drinking water (I don’t recommend for many countries) the water sometime usually “taste” different, such as when I went to Montreal Canada, I would describe the drinking water there to be “heavy.” It felt denser and harder to swallow from what I was used too, that was the case for the many different restaurants I went to when I was there. As well as Japanese water does not make good British tea.