She is a DF user, is almost imposible for her to start feeding sea Kings, wereas Shirahoshi is inherited power.

But yeah, in "theory", if she was able to dango all sea Kings, she would be like a Poseidón 2.0

In theory all you would have to do is lure some to surface with someone like Jinbe, snipe the dango into their mouths via Usopp and bingo your done!

From what I gather, the Seakings are on a different level to everything else.

Their minds are too wind and unpredictable, which is why even Fishmen/Mermen can't talk to them, except the 1 person.

Sorry but this is dumb first of all sea kings are in ocean water, the affect will go off with in seconds and second how the hell would she come close to shirohoshi unlike her shirohoshi does have to give a order or feed a dango to a sea king she can control them off bat