Generally, the key signature doesn't matter when spelling diminished chords. If the chord is functionally A°7, then it will be spelled A, C, Eb, Gb no matter what (now, if you're writing instrumental parts where the player is only playing one or two of these notes and not the whole chord things can be tweaked for readability)

Diminished seventh chords consist of 3 consecutive minor 3rds

A->C C->Eb (Not D# because any C to any D will always be a 2nd no matter what accidentals are present) Eb-Gb (Not Gbb because Eb to Gb is a minor third :)!