Okoye lost T’Challa twice. Yes, I’m saying twice because she doesn’t know that he survived yet in the first gif. Look at the first time and compare it to the second. She has composure during the Warrior Falls fight but completely loses it when T’Challa turns into ash. She lost her king twice. And no one is talking about it.
MAYBE WE WERE TRYING TO FORGET
Concerning the different reactions: There’s a reason!
She’s a political warrior. She didn’t just lose T’challa in the first clip. In a single instant, the entire politics of Wakanda shifted so that she now served under a man she clearly disliked. But she’s not allowed to publicly show her grief because she still serves the current king. She has to keep her composure. You can see how much she’s struggling (the tears in her eyes, the way her face is trembling) but she has to keep it together. She can’t show any opposition. Her duty is to the king and in public, she has to support him. Hence why she’s stoic in public but teases T’challa when they’re alone or with his family.
In the second scene, she’s technically in public, but A.) There’s no political opposition B.) Everyone turned to ash so she doesn’t have to hide her reaction because she’s alone and C.) S h e j u s t w a t c h e d h e r k i n g / f r i e n d t u r n t o a s h. Hence why she’s free to react with horror.