I thought a great skill that would be nice for a tank (could be good for Leona too cause she have a shield along with her passive but that's just an opinion ) :
"she puts a shield around her ally or herself that can soak up for all incoming damage taken from enemy champs. If the shield gets broken by that enemy champ who last hits it, she will rush immediately to that champ, using her shield (in a way that Pantheon does) to deal damage and stuns that target."
with that along with her passive Sunlight, her ally will be able to deal good damage to that enemy that got stunned.
What do you guys think?