While the Yu-Gi-Oh! anime is an incredibly fun show with a memorable cast of characters, one thing that the show doesn't do very well is female characters. There aren't many of them, to begin with, and many of them that are included aren't even duelists, but rather characters that support the male duelists.
However, basically every female character on the show has dueled at least once or twice even if they aren't a duelist by trade. Some are certainly better than others. A few of these characters don't even have a documented win under their belt, such as Vivian Wong from the KC Grand Championship.
Vivian Wong
Vivian Wong was one of the duelists invited to the KC Grand Championship, so it's clear that she has to have had some sort of dueling record. However, viewers never actually see her win any duels that she participates in on the show, losing to both Yugi and Rebecca during the tournament.
She's last seen dueling with Mai against the Paradox brothers in the series finale, but how that duel played out remains to be seen. Either way, viewers never see Vivian win a duel.
Ishizu Ishtar
Ishizu is a similar case, fans never see her win any duels onscreen. At the very least, we know that she won enough locator cards to enter the Battle City Finals in an attempt to help save her brother from his dark side. That alone is a pretty difficult feat to overcome.
Her only duel that takes place onscreen is against Kaiba in the Battle City Finals, and she almost has him, but Ancient Egyptian interference ends up clouding Ishizu's vision of the future and she loses the duel. It's implied that she has won before, but fans never see any of those take place. At least she has a few wins under her belt to set her apart from Vivian.
Serenity Wheeler
Serenity Wheeler does, in fact, duel once during the series, in a tag team duel. Along with Tristan and Duke, she takes on Nezbitt in the Virtual World arc.
This was her first-ever duel, and it shows. Despite watching everyone duel in the Battle City Finals, she doesn't know how to play a card in defense mode. Then, Tristan sacrifices himself to save her in the duel and she almost gives up, but she gets up and wins. Despite literally everything that happens in this duel, she managed to pull out a win, and is the first female duelist on the list to actually do so. This technically gives Serenity a 100% win rate. However, considering Tristan lost the duel and she only does compete in one duel throughout the entire series, that sort of negates that quality.
Mai Valentine
Mai Valentine is an interesting case in the series. She's the most prominent female character and is implied to be a great duelist. She makes the top four in the Duelist Kingdom and the Battle City Finals, and she's also shown winning various other tournaments throughout the series. Viewers barely ever see her win onscreen, however.
Besides besting Jean-Claude Magnum in a filler duel, she almost never wins onscreen. Sure, she's implied to be an incredibly skilled duelist who wins tournaments left and right, but viewers never actually see it. The second she comes onscreen, she loses. She even gains enough star chips to earn back all of Yugi's that he lost to Kaiba, but viewers just get the knowledge that she did win, they never actually get to see it happen.
Rebecca Hawkins
Rebecca Hawkins is the No. 1 rated duelist in America, and viewers do actually get to see her win on-screen a few times. This is all during the KC Grand Championship arc of the show (and Yugi does surrender to her in season one), during which she makes it pretty far before being defeated by Leon.
However, it doesn't earn her the No. 1 spot. That goes to an absolutely shocking character to be atop a list of duelists, Tea Gardner.
Tea Gardner
Tea is one of the only duelists to have a 100% win rate in the entire franchise, this is something that many of the protagonists don't even have. Tea duels a few times throughout the series. Fans are informed that she beats Joey time and time again in the early days of his dueling career, and she then goes on to defeat Mai in Duelist Kingdom to win Yugi's star chips (though Mai does surrender to let Tea win). Later on, she defeats Crump in the Virtual World arc of the show, but that is the last time that viewers get a chance to actually see Tea duel.
The No. 1 female duelist on the show has a win rate that is almost impossible to achieve. Yugi could never.