In regards to the dress code for women (and men), one might check out this official website for meeting the Pope:
PAPAL AUDIENCE DRESS CODE
One may note that wearing black or long sleeves are not requirements, but keeping the upper arms covered is.
BTW, when visiting the Dome of the Rock, my wife had to wear a shawl to cover her upper arms as well as a skirt or pants that reached below her knees, and us men had a similar requirement (not a skirt though-- gee, I wonder if a kilt for a Scottish man would be acceptable? Hmmmmm?). The only difference between us men and the women is that the latter also had to wear a head covering.