I agree with dl4fun that shurelya shouldn't be bought. I disagree though that it's useless since speed buff can help ninja nexus. Also, Frozen Heart plus Sunfire Cape is a bad idea since her W gives so much defense. You will be able to tank with this build but you don't do enough damage like dl4fun said. (Benefits per defense decrease the more defense you get. This build is going to be okay but Leona can be so much better in Dominion.)

Speed buff in dominion allows her to use her combo without being touched in return.
TLDR; she can jump in / deal dmg and get out before she is targetted.
There is absolutely no reason to build shurelya.Cooldown is even not required unless it gives you AP.
As her AP ratios are bad,it is wise to build Deathfire Grasp.
And levelling second skill is pure waste due to the reduced cooldowns that Q/E would offer.

PS: I am not saying that the build itself is bad. I am stating that it is useless in Dominion Game mode.
PS2: Defense 21? wtf :D

Sorry, but if tanks can't deal alot of output, theres no reason to target them. Put some AP items in there.