The marks on her collar resemble the mathematical symbols ∴ (therefore) and ∵ (because), leading to the theory that they represent her "Ability to Manipulate Fate""S" or "6" shaped brooch.
Fan art often depicts one of the below decorations.
The first, aristocratic-looking one is apparently called a "Jabot".
The second is a necktie-like ribbon to match Flandre.Bat wings are evolved from palms.
The upper protrusions correspond to human thumbs.Though hidden and unseen, it looks like she wears a suspender skirt.A made-to-order garment with slits in the back to let her wings out.Reference: The Great Touhou Project Exhibition
Bats are so interesting! Their ecology and conservation methods are surprisingly unknown.※Contains multiple headcanons and points of speculation
