In the previous film, Queen Ravenna had a very close, somewhat mystical bond with her brother Finn, who was her head enforcer. He is also seen during a flashback to when Ravenna received her magic powers. This film, however, makes absolutely no mention of him in either the scenes set prior to the first film or the ones set afterward. In addition, there is no indication in the first film of Ravenna having any other siblings besides her brother.
Queen Ravenna asks the mirror who's the fairest of them all, and it replies this will be Freya's daughter, though Snow White was already alive. However, that simply means had she lived, the girl would've been even more beautiful than Snow White.
In the first film, Ravenna's brother, Finn (played by Sam Spruell) taunts Eric (played by Chris Hemsworth) about his wife's death. He implies that he is the one who attacked and killed Sara while Eric was away (off to war). In this film, however, as Freya's trick, Sara is shown to be killed by a fellow huntsman before Eric's eyes.
Young Sara has a face full of freckles. Older Sara does not (as Jessica Chastain has a clean face). Freckles can fade with time, especially in a land with little sun.
When Sara and Erica are in the woods after recovering the mirror and he is convincing her that they belong together, she is tending to and has visible wounds on her shoulder and arm. When they begin to make love, the wounds disappear. In the morning, they are back again.
At the Winter Palace, just before he tries to jump, Eric pulls out an axe. Later after having failed the jump and crashed on the roofs, he safes himself with a axe that has a very different blade. The axe shown in the beginning would not have been able to grab the edge of the roof.
How did Freya regain her youth and beauty? She looks the same as when Sara and Eric were just kids, and ten-fifteen years later when they are adults, so Ravenna and Freya should both be very old. But on the plus side, they are very powerful (if evil) sorceresses.
When they're separated by the wall of ice, Eric sees Sara being murdered by Tull, and from her POV she sees his agonized reaction as he tries to break through and save her. However, since the ice wall was magical, from Sara's POV she should've seen Eric turning away to abandon her, as was shown much later on in the movie.