Permanent and controllable angel, with unique powers like, for example, when you cast your Halo, Cascade or Divine Star.
So does she, but then placing her and moving her can be profitable for you in a raid when Halo will spread out from you, and from the angel, for example. That could be the unique power. Outside of that, she smites your enemies and in return, that will heal the lowest health member in your group or raid. Like a mini version of atonement.
Best part with this controllable angel would be she copies your Haloy, Cascade or Divine Star, you cast it - she cast it.
But it does like half of the original healing it does for you, when she casts it. So placement can be something that is not needed always, but can be fun to be good at (at least for Halo).
Maybe you got some ideas for abilities that would be nice for such thing like this?
New model that looks more like this, perhaps more darker..
http://th02.deviantart.net/fs71/PRE/..._a-d6mlmh8.jpg