I thought that the paper bombs didn't all go off at once but in the span of 10 minutes. So she could have activated a smaller amount (it is still a large figure mind you) but then those bombs would activate other bombs and so on.
She did it to trap Obito. The paper bombs were set in a huge hole, causing them to explode one after another and thus kill Obito/Tobi after his Kamui time runs out. She could've detonated only one paper bomb, that would explode and detonate another and so on.
Something like a domino effect.