I believe that the act of murdering so many innocents in this last battle was deserving enough to earn the title of a tyrant especially when the bells of surrender had been rung by the commoners.
As for being betrayed by Jon, the writers did give a good enough reason by showing that she wanted to still continue warring and conquer other lands apart from the seven kingdoms.
As for Sansa being ungrateful, one can see that she did not approve of being ruled over by any King, even if it was her own brother. Her reason for that wasn't just distrust for Dany but a general feeling of hate and disgust for the position itself because of what she had endured in her time at the capital and even after that until she reached Winterfell back. So she probably didn't want to trust the chair anymore and wanted to keep her independence whether it was Dany or anyone else sitting on the throne, even if it was his own brother.