Gabrielle would win and here’s why I think that. First of all Xena cares very much about Gabrielle, some would even say loves her, and would not willingly hurt her in any way. While I think Gabrielle also loves Xena, I also think that Gabrielle regards Xena as being much tougher and more skilful, so I think Gabrielle would be more willing to fight with her full strength whereas I think Xena would hold back and pull her blows.