My sister has developed otitis interna. what is it exactly?

Otitis interna?: Otitis "interna" is not a standard medical term. The most common ear infections are "otitis externa" (swimmer's ear), or "otitis media" the common ear infection of children. An "internal" ear infection would apply to the inner ear structures, of which the most common infection is a viral process involving the 8th nerve which causes vertigo ("labyrinthitis"), mostly resolves on its own.