It just so happens the executive producer of 'Arrow', Andrew Kreisberg, is the creator of the DC Comics character known as Cupid. He introduced the villain when he was writing the Green Arrow/Black Canary comic series.
Here's what Kreisberg said about Cupid to EW -
"I always loved the idea of Green Arrow having a crazed fan. When I was writing the comic book, my big goal was to create a villain who would last. Cupid has since appeared in the DC Nation shorts on Cartoon Network, and to have her fight our TV Arrow is so much more than I ever could have hoped for the character.” - Andrew Kreisberg
This just in—@CW_Arrow casts 'Supernatural' alum as lethal lovestruck fan: http://t.co/r260uouOW1
— Entertainment Weekly (@EW) August 29, 2014
Season 3 of ‘Arrow’ premieres Wednesday, October 8.