I have a feeling that she won't be wearing black leggings, but large black boots instead
You are correct, she's wearing boots. The artist probably drew this based off the frontal image which gives the illusion she is wearing stockings and black shoes/boots. But in the side view we can see she is wearing knee high boots with no stockings.
I think she may be wearing a full dress, and possibly a longed sleeve shirt underneath it. --- GLAD GANG l SSS l No.XII l OPBW2C-Wargle I R - Zarren I am the Anti-troll. Your poll needs a bacon option.