To be clear, this Twitter user is not the original source of the Fear the Walking Dead poster theory, and the post doesn’t include the poster of Karen David’s Grace, who was also seen with a tear streaming down.
And I also understand that Grace technically didn’t get to know her stillborn baby, the fantasy sequences in the episode “In Dreams” made her relationship with Athena feel genuine.
Still, it gets the point across well enough, which is that the tears seen on the faces of Grace, Jenna Elfman’s June, and Zoe Colletti’s Dakota are very likely indicative of their mutually exclusive grief over losing those closest to them.
While it’s true that Dakota’s love for her sister-mother Virginia had run cold by the time the latter got her head blown open, they had a long, mostly loving relationship that preceded the downfall, so it’s not SO out of character for Dakota to cry about it.