Comment below rating threshold, click here to show it.
Theorycrafting so don't be mad.
Sure she's got a charge but her ganks won't be that strong cause she cannot gap close as effectively as say Maokai or Rammus. She has no hard cc like a stun and a more reliable Ultimate stun like Leona's.
She definitely will be effective through terrain battles where she can get the initiate through walls or cut off unorganized teams so that they cannot get back together. Her frost auto attack will require skill and the tank to prioritize who to hit.
She doesn't have a real defensive skill that can allow her to tank though.
Counter tank champs say like Alistar would probably keep a Sejuani away easily.