I think magical-girl would make sense to include, as the common term for a fairly popular theme. There's a magical-realism tag, but while they have some overlap, they are definitely different things. Currently 67 projects use magical-girl unofficially, vs. 112 for magical-realism.
I'm kind of struggling with duplicate tags. There are several sets of tags that have very slightly different connotations, such that one project might justifiably want to use one tag but not another, and thus might not be considered candidates to merge; but in many cases, a project would want visibility from the whole set, because for that project, those tags all cover identical ground. We only get ten slots for tags, so while I understand wanting to subdivide for the sake of precision, it is also frustrating to have to pick and choose between multiple extremely similar tags, knowing that search results will be split between all of them.