There are several reproductive disorders that can present very similar. Without further investigation it's hard to know which one and it can sometimes be a "combination". For instance EYP can be accompanied by Ascites.
Your question of why her wattles and comb turned dark purple, my guess would be lack or reduction of oxygen as she was passing.
I'm very sorry, it's heartbreaking to lose a favorite. It is nice that you did get to spend some time with her though.