When King Agdar and Queen Idun took Anna and Elsa to the trolls for help, Grand Pabbie erases Anna’s memories of Elsa’s magic to be safe, believing it’d help prevent another incident. This is something I’ve never understood and it’s one of the things I do not like about the movie. While I understand wanting to take precautions, this later only served to make the matter more difficult, not less.
The only guess I’ve ever been able to come up with is it being assumed erasing Anna’s memories would prevent her from asking Elsa to “do the magic”. However, no one took into account it wouldn’t stop Anna from frequently asking her sister to play with her and as Do You Want To Build A Snowman proves, it certainly didn’t. If one thing can be said about Anna with certainty, it’s that she’s persistent.
However, if the sisters were going to be separated, it still seems useless to have erased Anna’s memory. Either way, she was going to ask Elsa to play with her, so what difference did it really make? This precaution was unnecessary.
There’s also the possibility it was to erase trauma from her mind. We saw how heavily the incident weighed on Elsa. Perhaps it would’ve weighed just as much on Anna’s shoulders, especially since it came out of recklessness (her not slowing down when Elsa was telling her to). That may make the decision to erase Anna’s memory a little more understandable, but couldn’t Grand Pabbie have just removed that particular incident if that was the case? No trauma and everyone can just explain to Anna (and Elsa) she needs to be a bit more careful when playing.
Perhaps I’m simplifying this too much? I’ve always thought their childhood incident could’ve been handled so much better. Of course, parents (and grand-trolls) aren’t perfect and everyone makes mistakes, so that’s a bit of a silver lining for me. Getting to see that parents aren’t perfect. Perhaps if Anna and Elsa’s parents had a second chance, they’d do things differently.