User blog comment:7-45 Fire/The Roxy question/@comment-29197449-20170622025225

She's not. She was actually planned to be the seventh Winx as there's even a Season 4 episode called "7: The Perfect Number" but, because Rainbow basically slated her in Season 5, there's no chance of her being a member of the Winx. Heck, Bloom even stated that Roxy was a Winx in Roxy the Seventh Fairy, but that's a comic issue and the comics always revert back to how things are in the main series.

Bottom-line: Roxy was going to be a Winx but didn't for whatever reasons Rainbow had.