Vane, n. a blade or plate to be moved by the air (e.g. a weather vane)
Vain, adj. conceited or futile or without value
Vein, n. a section of a branching system that carries liquid or forms a framework
Jill stepped back from the finished piece, evaluating it with a critical eye. She had crafted each vane to resemble a maple leaf, complete with the delicate veins extending along the leaf. Although she knew others might consider her vain for saying so, she was proud of her hard work.
NB: The idiom in vain means to no avail (i.e. a futile effort) or in an improper manner (i.e. without proper value).
The idiom in that vein means of similar kind (i.e. in the same piece, section, or framework).