There are two extra versions of Sheva to unlock for the mercenaries mode in Resident Evil 5.
The first is Clubin Sheva, which is unlockable by getting an A rank on Ancient Ruins in mercenaries mode.
The other outfit, Tribal Sheva, is unlocked by getting an A rank on Missle Area in mercenaries mode.
Getting an A rank requires either 40,000+ points in single player mode, or 80,000+ in either co-op mode.
If you’re looking for some help for the mercenaries mode, check out my mercenaries mode strategy guide.