No Hilary is not the one who should be the fifth Bladebreaker but keep guessing if you're playing along.

Hilary was introduced as the no nonsense class president known as the Wicked Witch of 8th Grade back in V-Force, but found that she was getting dragged into Tyson's beyblading world the longer she was around him, this would later lead her to becoming the coach of the Bladebreakers after suggesting the team goes back to basics when the magnacore was introduced in V-Force, this was backed up by Kai, since then she's stuck by ever since with her only attempt at blading being a humorous moment attempting to be an idol.
I bring up Anzu from Yu-Gi-Oh as their roles are very much the same, a good cheerleader and a supportive friend, just a pity that they add absolutely nothing to the series and doesn't really make a good case for female characters in the franchise.