I just finished reading the last chapter and it sucked because Kumagawa isn't there. Honestly, this is the first shounen manga where I really disliked the MC. If it weren't for Kumagawa, it would've sucked really badly.
And no, she isn't invincible. The manga is only mocking the shounen genre. They keep commenting on how fast she is and that she is faster than light (yet ironically, they still can see her and talk while she is in the middle of her attack) yet her fastest attack only barely broke the sound barrier.
Besides, if you finished the manga you would know that she was (some spoilers ahead):
Defeated by Iihiko. Also, her skill has a huge weakness. Once you take out her eyes, she loses it along with all her abilities. She also can't copy anything. She couldn't copy styles which means she probably can't copy many things that are the source of the other Shounen manga characters. For example, she most likely can't copy any devil fruit ability from OP for many reasons that should be obvious. Seeing that, If you say she's invincible, how can she beat an OP logia user?
She absolutely can't beat any of the DBZ characters, almost none of Bleach's main character's, and none of the top 10 Naruto characters, same goes for One Piece.
Besides, she lost almost all her skills by the time she was in her mid twenties.