i think the reason for dany’s “blank” reaction to viserion dying was because she never really thought any harm would come to them. like why would she? she’s seen drogon get hurt like twice already and he is fine. she had no reason to believe the white walkers had anything to harm her dragons. her looking there “emotionless” is just her being in shock that one of her “invincible” dragons died. it’s a huge shock for her, of course she froze up.