Supposedly she is supposed to dual wield but I've given her 2 maces and she only ever uses one of em. Does she only dual wield with a certain type of weapon?

She's dual wielding Dawnguard axes for me and before that 2 forsworn swords. Try giving her swords or axes?

In vanilla PS3 Skyrim, she will dual-wield any axe-sword and axe-dagger combinations, she also likes two-handed axes and bows.

PS. Give her an elven axe and an elven dagger and a forsworn bow with simple iron arrows and she will make wonders...