Once she outgrew the heirloom items, I stopped transmogging her and she just wears the quest reward upgrades. So, yes.. she's been wearing dresses. *sigh* I hated how dresses looked on her, but now, now I think I must be used to them because I think she looks cute.
Here's Roo at her 85 dinging, everything she has on is from quests in Uldum, I think.
Shoulders: Vir'naal Spaulders
Chest: Robes of Khintaset
Hands: Keythief Handwraps
Waist: Girdle of the Rescuer
Feet: Incorporeal Sandals
Staff: Ihsenn's Staff of Terror
I thought I'd really hate how all the quest rewards seem to look the same, but it really helped - I know if she had something that clashed I wouldn't be able to keep myself from mogging her. Plus, it seems silly to keep mogging her as she levels and gets updated gear so frequently.