Do te think Elsa's character development is unrealistic?

No,I do not think so. It does look realistic

personally, yes. i see elsa as a person who has social anxiety and depression which causes her to be unable to fully control her abilities. her finding out that the way to control it is through Amore is an okay concept, but the fact that she's able to have full control over it so quickly is a bit ridiculous in my opinion. i think that mostrare her practising it with "love" would have been a better end to the movie.