The Lævateinn that Flandre is holding in her older Sprite is very different from the Lævateinn that she's holding in her new Sprite. (See on right).
Flandre's Second Spell Card (Taboo "Lävatein" or Lævateinn) shares its name with the sword (wand in some versions) of Loki, a Norse god known for causing mischief. This sword/wand is used by the fire giant Surt in Ragnarok (the Norse equivalent of the Apocalypse) to burn down the whole world, except for one safe haven. Fitting that Flandre would be wielding a tool of such destructive might.
Her boss theme ("U.N. Owen was her?") and her second-to-last spell card ("Secret Barrage - And Then There Will Be None?") are references to Agatha Christie's novel And Then There Were None (also published as Ten Little Indians). U.N. Owen (which the characters of the novel naturally deduced to mean "Unknown" and also recognized as referring to Mr. Owen's wife) was actually seen in person in that thriller but was only revealed at the end.
Flandre was born in 1507 A.D., according to Gensokyo's timeline, and holds the distinction of being one of the few characters whose birth year is known, along with her sister and Toyosatomimi no Miko.
In Perfect Memento in Strict Sense is stated that when Flandre destroy the "eye" of something or someone, she actually erases the existence of the thing (breaks) or person (kills).
While it is a matter of course, she has the destructive power of oni and the nimbleness of tengu, as well as a vampire's bodily and regenerative ability. She somehow exceeds even her older sister Remilia Scarlet.
Flandre's wings have an unusual appearance which bear almost no resemblance to a vampire's typical bat-like wings (or even organic matter). It has been speculated that her wings are artificial and that she fashioned them herself and then attached them to her body. She may have lost her original wings or been born without them.