In the main story, it is shown that Rem falled in love with Subaru, but it was something more healthy, and she could still think critically over the main character's actions.
But in this movie, the love of Rem for the main character is way too exaggerated. She'd always say things like "You're incredible" when the main character proposes anything, being Ram the only one of the 2 to think critically.
Such a personality change doesn't make sense at all, since the movie happens around the half of the story, when Rem was in love for Subaru but not so much.
The movie is overall funny, but it's not really necessary to watch it since it doesn't really brings anything to the plot, and is not very goodly made.
