Leia did once fight a Hutt with a lightsaber. It was in the expanded universe novel "The Planet of Twilight".
Beldorion the Hutt was the only Hutt ever to become a Jedi, but unfortunately, degenerated into evil and madness after surviving Order 66. After conquering a planet called Nam Chorius with another corrupted former Jedi, he became as bad as any Hutt.
Until, that is, 13 ABY, when Leia came there looking for fellow Jedi trainee Callista Ming, who had been taken prisoner by Beldorion. The same thing happened to Leia, but... She wasn't going to let this turn into a repeat of the mess with Jabba. She managed to get loose, get ahold of her lightsaber, and confront him.
He didn't go down without a fight, of course. Possessing strength and agility unheard of for his species, he used a lightsaber quite effectively against Leia. She even commented to herself about how fast he can move for such a massive creature. Ultimately, he lost, leading to a very... graphic description of what happens to a Hutt's body when it's sliced open by a lightsaber.