Light based AO is too much a "one size fits all" type of solution - which almost never works.
You're better off with material based AO. For example, you DON"T want AO on those transmapped eyebrows, but you DO want it on the stones of that flor, and probably on the skin of her body.
The AO strength on materials should be set about 10 times as high as on lights to get a comparable effect, that's some weirdness that's built into Poser.
You'll also want some shadow and some specular effects.
IBL is great for setting the overall lighting of your scene, but you need additional lights for specular effects and shadows. This looks like an outdoor scene, so I'd suggest adding an infinite light for "sunlight" and shadows, toning down the IBL light strength a little, and maybe an extra light with Diffuse color set to black, Specular to white, no shadows, to bring out some extra speculars.

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