"She lives in Philadelphia."
Translation:Ea Philadelphiae habitat.
But in authentic Latin, often you don't know he/she/it without examining the surrounding context. (And the need to know that information is an English need, not a Latin one.) By that reasoning, we need to always write "is" when the subject is "he" -- which certainly isn't the situation in Latin texts.
"Philadelphia" is the nominative form (used mostly for subjects)
"Philadelphiae" is the locative form. Locative is a case which exists only for the names of cities and small islands (+ a handful of common nouns such as "domus") when talking about a location where the "action" is taking place without movement.
Here are examples:
- Philadelphia is a city => "Philadelphia" is the subject => We use the nominative case for it ("Philadelphia") => Philadelphia est urbs
- She lives in Philadelphia => "Philadelphia" is a city where the action is taking place without movement => We use the locative case for it ("Philadelphiae") => Philadelphiae habitat