Winneuse is the feminine french version of a “winner”. It would be “winneur” for a male.

Une winneuse would be the feminine form of slang term “un winner”. The usage of this word by native French speakers is, in my experience, generally sarcastic — it doesn’t usually mean “someone who wins”. It can mean someone who really lucked out (“avoir de la win” is a slang term for being lucky, opposed to “avoir de la loose”, pronounced like “looz”) or someone who is really stupid (“il a une bonne tête de winner” means “he looks so dumb”, as in able to win a dumbness contest). Having more context would be useful to be able to really help.