contraction vs full form - "Isn't that..." expanding to "Is not that..."

Sorry if this has been asked (multiple times) before already, but it's one of those things that's extremely difficult to search.

Basically, my question is whether the use of "isn't" in sentences of the form "Isn't she lovely?" a rule, or an exception to a rule?

Because if you expand the contraction out, then you have "Is not she lovely?" which is obviously(?) wrong. You would say "Is she not lovely?" I think...?