Universal ally

Everyone's best friend.

While it was true that Jesse couldn't find a better friend than Nadia, it was also true that neither could Jesse's worst enemy. If Nadia was also an ally of Jesse's worst enemy, then Nadia was playing both of their sides plus everybody else's she collaborated with, not that she couldn't collaborate with who she liked to collaborate with. Usually though, a friend of your enemy is not your friend, even if a universal ally is what they seem to be.