For the male side, a theory is going around that Mangle is a male because even though it's in Ladies Night, they think that it's there because without it the night would be way too easy.
There is evidence supporting both sides. For the female side, a theory is going around that Mangle's a female because it looks girly and pink and because it is in FNAF 2's ladies night.
I guess it's a female but Mangle is supposed to be the toy version of Foxy therefore I'm guessing that Mangle is a male. It hasn't been confirmed but for now I vote for both sides.