"What is her address?"
Translation:Cad é a seoladh?
It's not dumb at all! Nouns are lenited after 'a' when it means 'his', not 'her':
His address: a sheoladh
Her address: a seoladh
Their address: a seoladh (if the noun started with b, c, d, f, g, p or t it'd be eclipsed after 'their')
For more, see https://www.duolingo.com/comment/10995361