Reached Mahidevran's arrival to the palace and her conversation with little Mustafa in the gardens. It has to be said that while I have my gripes with Mahidevran's character, it mostly boils down to two points which are very openly and clearly showcased in this scene: Mahidevran's foolish naivete and her faulty upbringing of Mustafa.
From this moment on one can see that Mahidevran perceives her son to be the heir to the throne of Ottomans in how she openly claims Topkapi Palace, naming it hers and Mustafa's along with Suleiman's. When Mustafa speaks these words while he and Mahidevran are greeting Valide Ayşe Hafsa, it can be seen in how Valide immediately disciplines Mustafa to not say this and how she scolds Mahidevran for teaching these ideas to Mustafa, that these ideas aren't proper - Suleiman is the ruler, the ultimate authority, and Mustafa - even while being the only son at this point (show-wise at least) - is in no way due to the same privilege.
Mahidevran's naivete in this case is strongly shown in how she doesn't see the issue in Mustafa's words and behavior of him trying to command his grandmother and aunt and claiming the palace as his own - following his mother's words. In such a system as Ottoman Empire's ruling family, there must be no challenge to the ruler, not even from his own children, and Valide Ayşe Hafsa knows this truth well - and to see Mahidevran act with such naivete and foolishness is a disappointment she scolds Mahidevran for. In similar fashion, Mahidevran wasn't preventing her son's improper behavior at this one instance, showing that in her view of Mustafa's upbringing such misconduct isn't a mistake. She assumes things, and without people to sit her down and thoroughly explain why she's wrong, people to hold her accountable for the mistakes, she continues to have those misgivings which to later larger conflicts.
Mahidevran's misfortune in early episodes is in in many cases self-inflicted by the naivete and foolish belief that everything would be as it was before in Manisa. To be true, I pity this Mahidevran of this time: she couldn't accept the changes, couldn't learn to accept her changed place as Valide was instructing her to, but I can't blame her for her anger. It is only natural to desire that your partner be loyal to you, and that the system they live in from the very conception of itself supposes lack of said loyalty to be be a given default, which Suleiman sees no problem with, is the reason for Mahidevran's misery in early episodes. I'd assume that in Manisa he had been mostly preferential towards Mahidevran and she had grown used to being the one he's loyal to as she perceived it, but as far as I can see and understand this situation, it wasn't loyalty to Suleiman, but merely preference. Her misfortune in earlier episodes was caring too much about that man's love and desiring it, instead of prioritizing herself and her son as Hafsa was teaching her.