"because it is she that I have watered": not "her"? [closed]

In the book The Little Prince, there’s

because it is she that I have watered; because it is she that I have put under the glass globe

Why “she” instead of “her”?

Solution 1:

One of those old rules of English grammar based on Latin grammar stated that 'nouns in apposition' (when we say A is B) must be in the same case. So it is strictly correct to say "It is I", though most people in everyday conversation would say "It's me".

The translator used a rather old-fashioned style, then, though as the flower (a rose, wasn't it?) is the object of the attentions it does seem odd to use she and not her.