The problem with this sentiment is that "The Queen of Pop" is literally Madonna's nickname. It was given to her by the media and culture in general, just like Michael's "King of Pop" and Ozzy's "Prince of Darkness," it's not a title that female singers compete for. It's Madonna's title, full stop.
And even if the title of "The Queen of Pop" were something you compete for, Madonna would still have it. She earned that title because of her all time impact and success, it doesn't matter if some other girl is bigger than her at the moment or for a few years. None of them are going to match, let alone exceed, her overall fame, success, and impact.
Elaborating on the point of all time vs. at the moment when comparing two or more acts, longevity and consistency trump peak. Madonna released 'Hard Candy' 25 years, as in a full quarter century, after her self-titled debut was released and yet it sill moved 3.5 million globally. Mind you that was despite it not being a 4th quarter release, and the fact that she and Warner Bros. only put notable effort in to the first single. That first single was a global smash and then the 2nd single went Top 10 almost everywhere. And of course we all know how the subsequent tour fared.