I played this over and over many times. Sounds like she is saying "tia" rather than "dia". I know Duolingo comes up with some weird/nonsensical phrases sometimes, so "What a cold aunt" didn't seem very unusual.
I think if it were 'tía' then it would make more sense if Duo was asking you to translate 'what a frigid aunt!'. But let's not go there.
'tan' was not needed! My answer of inserting 'so' was incorrect! C'mon Duolingo!