It was not just her weapon, she basically did it on her own after a brutal battle, a great one with good tension, great cheoraphy and good artstyle overall with a great enemy for Nami:
These are the panels before she use the weapon, she did it on her own power, stop the attack with taking a painful attack.
Overall should I showcase the whole fight again? Just compare the fight with Miss Doublefinger vs Nami fight with Ulit..
Full fight with Doublefinger for these one who actually forget how much time and insane work Oda did with the past strawhat battles:
That was Nami first big battle on her own, a battle who had anything.
Gag scene, Nami as character growing, as fighter growing, a good enemy with interesting moveset, cool attacks from both side, tricks like Nami making illusion, a very hard battle for Nami where she go over her limit, where she himself need to put the work in the end.
Great artstyle, a full fight who take over 4 chapters next to next, Oda make a great set up and end a great battle.
Same with Kalifa, Oda spend at least chapters and good battles.
Where both villian and protagonist show skills and interesting moveset, great matchups.
And now compare that what we get in the past with Ulti and Pageone vs Nami and Usopp...
Pageone barely show anything, dude has legit not shown any attack, Ulti had just one move, something liike interesting moveset with different skills in new world where haki and df can play a big role and all what we get is this?
I going to debate with anyone who wanna try to say me that Ulti+Pageone vs Nami and Usopp is actually a great battle, it isn´t it. No tension, no feeling, running over running, offscreens... Missdoublefinger show more then Pageone+Ulti did together.
And we wait 400chapters,10 years of hope for Nami to get again a real good battle, but nope, Tama is more important, Tama is actually stealing the show of the strawhats(even Ulti pointed it out this chapter lol).. The strawhats who let start us to read this manga get threat like side characters while side characters actually get threated better with far better panels(Scabbards) or Tama who has right now more screentime then King,Jinbe,WsW together....
Oda introduced too many characters and had to cut time from the SHs fights to make up for it. He should either ignore the background characters or not introduce some of them. The Yakuza bosses should have been either killed or beaten badly by the Tobi Roppo off screen so that they wouldn’t waste panel time and the Tobi Roppo get some hype, just like how the Mimawarigumi existed just to hype Hyo. Apoo and Hawkins didn’t need to be created at all. None of the Gifters/Headliners deserved any spotlight at all in Onigashima besides Bao Huang. Marco should have been fighting the BMP that BM brought with her mostly off-screen, minus Perospero who fights Carrot, and that way King and Queen can start fighting Zoro and Sanji sooner