I haven't seen too many decks with Relia in them, probably because she just isn't great. But hey, we can fit her in somewhere. I took a gauntlet deck that someone came up with and modified it a little to fit Relia.
Reaching high power levels is key to this deck, achieved through Copperhall Porter, Icaria, Spire Chaplain, and Marshal Ironthorn, and, on the rare instance, Relia herself. Marshal and Icaria especially help you play your big units earlier than you would otherwise. All the power really buffs Mantle of Justice as well.
Most of the units you lay out are threats and so most are quickly removed, which makes it so your later units, such as Marshal, Rolant, or Relia can stick. Perhaps the best unit in this deck, however, is Silverwing Familiar - a great holder for your weapons (especailly Mantle of Justice) and, of course, a great combo card with Hero of the People.
Crown of Authority, Rolant, and Relia are the finishers for late game situations, though this deck often wins before they can come out, making them a little bit irrelevant, sadly, but Rolant especially has been useful for surprising permafrost-using and non-shadow/justice decks. Often no silences/kills are left.
As for how useful Relia has been, the answer is not too much, but every now and again she gets in a winning hit. That being said, either we win before she comes out, or she just isn't useful when she does arrive. I'd probably prefer two more Rolants, but I only own 2. If she cost 1 less, or provided a justice sigil with more power already in hand/play, I think she'd be golden, but as it is, she works, but isn't optimal. Nevertheless, this is a fun deck and I hope you have fun playing it.