Here’s the thing: You can’t copyright an idea. So as long as you’re writing the work yourself, it’s not plagiarizing.
So you can retell or reimagine a Cinderella story or Pride & Prejudice or even Twilight.
BUT it has to feel new and different or people won’t want to read it. You can’t just retell Twilight. You can be inspired by the concept and tell your own story of a girl falling in love with a vampire or a girl falling in love with an overbearing rich man and set it in a big city and throw in BDSM (oh wait, someone did that).
Same with fairytale retellings. The ones that work are the ones that are different, that have something readers won’t expect and that keep them wondering what will happen.