One of the areas in the fictional female character's life that needs to be considered when trying to write, for lack of better terminology, a "strong female" is relationships.
Flags. It's a seemingly simple concept: a piece of cloth with a design on it that represents something. Simple, right?
Because we all use them.
Media, unfortunately, often dictates how certain groups of people are perceived in society. This is why representation is so important in TV, movies, and books. This need for representation goes beyond just race, gender, and sexuality. It is also important with personality types and niches of humans. For instance, the way awkward characters are treated is often a misrepresentation.
But everything has flaws in it, and Harry Potter is no exception. To me, the most annoying was her use of dialect, primarily with Hagrid.
A strong female character in fiction is often seen as a set personality - cold, vicious, doesn't take any BS type of girl. But why?
The number one problem with romance, as I said above, is when the chemistry seems forced. When two characters are forced together for no reason other than because they need to be in a relationship, it comes across as... well, forced. Force relationship are dry, and much worse than letting characters stay single.
And suddenly those character sheets go out the window.