Why didn't Daenerys order this character to stay out of the fight?

Question

In "The Dragon and the Wolf" (Game of Thrones, S07E07),

Jon tells Cersei he can't stay out of the war because he's already sworn allegiance to Daenerys.

Afterward, Daenerys tells him that she respects his honor to his word, but she wishes he had just promised to stay out of the fight. This question explores why it would have been a bad choice for Daenerys to release him from his oath, but why didn't she just order him not to fight in the war, without releasing him from his oath of allegiance?

Since he's sworn allegiance to her, isn't he honor-bound to follow her orders?

Cersei said that she wouldn't trust Daenerys's word but that she would trust Jon's, so I'm assuming that would include the case where he follows Dany's orders not to fight and gives his word that he'll do so.

Answer 1

It isn't just about fighting. Cersei gave them 3 conditions regarding Jon:

He will remain in the North where he belongs.

He will not take up arms against the Lannisters.

He will not choose sides.

Perhaps Daenerys could have Jon swear to stay in the North and not take up arms against the Lannisters, but the third condition cannot be met. Jon has accepted Daenerys as his Queen, and he is no longer an independent King.

Cersei has very few cards left at this point, and a great army is not one of them. One she hopes to retain is legitimacy - Daenerys was raised in foreign lands and brought foreign armies to conquer Westeros. Remember that this already cost Daenerys the potential allegiance of a Westerosi Lord, Randyll Tarly:

Say what you will about your sister, she was born in Westeros. She's lived here all her life. You, on the other hand, murdered your own father and chose to support a foreign invader. One with no ties to this land with an army of savages at her back.

What Daenerys has that cannot be taken back is the allegiance of one of the remaining great Westerosi houses (and the entire North with it). It legitimizes her. Cersei is still playing "the game," she's losing, and this is another huge blow.

Answer 2

Telling Jon to stay out of the fight is exactly the same as releasing him from his oath. If he's out of the fight he might as well not be following her as he will have no say in the deciding outcome of the wars.

As such her reasons are also the same as the linked question and the answer from @GhotiandChips:

Daenerys could have released Jon from this oath on the spot, but that would be problematic:

• She has spent every episode since the two have met trying to get him to "bend the knee" and swear fealty, and every time she was met with stubbornness and a word about honour surrounding being the King in the North - for her to give up that earned trust and sworn vow, shortly after the effort it took to establish a good relationship and a trust to pry through Jon's stubbornness is probably not worth it, in her eyes.
• That meeting between the two major parties is all about displaying power and strong resolve, and is highly cerebral. For Daenerys to surprise Jon by relinquishing his oath and dishonouring him would cause a confusion within their party that would display a weakness that Cersei can detect and think about exploiting, and it would prove to all the witnesses that this is a weak union keeping that dynasty together, if it can fall into confusion on a whim. In this game of mental chess that is this meeting, it would represent a disadvantage.
• Daenerys would lose the respect of her supporters. When Joffrey had Ser Barristan Selmy "dismissed", it was a very controversial move that many considered a reflection of these awful rulers, but they couldn't do anything because they feared them, and that was a relatively small dismissal (Kingsguard oath vs a kingdom's fealty to the crown). Most of Daenerys' followers choose to fight for her because they believe in her, they have a lot of faith in her resolve and invest a lot of respect and love into her words and actions because she is true to her word and her resolve is strong. To suddenly force Jon to go back on his word this way would risk her losing the respect of her followers, which could, in turn, damage her relations with the people that would fight for her.
• She is in love with Jon Snow. Not only does she experience flattery, honour and appreciation when the man she loves stands his ground expressing his loyalty to her, but she also knows that insulting Jon by forcing him, through royal power, to go back on his word and break his oath, especially after Jon says the following:

JON: When enough people make false promises, words stop meaning anything
_{—"The Dragon and the Wolf" (Game of Thrones, S07E07)}

Would be pretty close to breaking Jon's heart. At the very least, it would damage their relationship, which her heart obviously doesn't want to happen, given her affection for him.

Answer 3

why didn't she just order him not to fight in the war, without releasing him from his oath of allegiance?

You're missing some key points here.

• Cersei asks Jon to remain impartial, as a way to prevent either side (Cersei/Daenerys) from trying to gain favors with Jon in order to get his allegiance (keep in mind that, at this point in time, Cersei thinks the North is not sworn to anyone).

• Jon mentions that he is sworn to Daenerys.

• Cersei storms off. Daenerys speaks to Jon about not having said that.

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Jon going back on his words would be meaningless to Cersei.

The damage is already done. Even if Jon would want to go back on his promise to Daenerys, and he sticks to his promise to remain impartial, what is preventing him from allying with Danaerys again when the truce ends?

Cersei knows she's lost Jon's allegiance, and he will never bend the knee to her.

After Jon reveals having bent the knee to Danaerys, everyone (Daenerys, Jon, Cersei) is aware that Jon's words have made an impact that can never be taken back. This is why none of the characters even suggest Jon takes back his words, they only say that they wish he hadn't done it in the first place.