If the author has any idea of real history, then the book will only become trouble for Shizuku because they'll realize she's from the future and demand she produce the weapons. All the modern tools and techniques Shizuku brought have been doable with 16th-century engineering. High-pressure guns that work are simply outside the realm of possibility. The metallurgy to make them (not to mention the raw materials) won't be available until the 19th century. For that matter, no one in the 16th century knew how to make thin metal casing reliably. Shizuku knows farming techniques, but advanced metallurgy should be way beyond her ability.
Some improvements to existing weapons technology should still be possible but may not be economical. Fulminate is doable. This may allow the use of percussion cap two centuries early, although making the caps themselves might be tricky. Rifling is doable, and casting Minnie bullets is not actually that hard (standardizing them is). Obturating casehead is way outside the realm of possibility, but a non-obturating thick-walled case like the 1812 Pauly should be within reach. This should allow her to make something like a Pauly inverse break-action breech loader, but that should be the extent of her ability in this era. Plus, something like that can't possibly equip a sengoku army given the sheer cost of the gun and ammo.
That said, Japanese arithmetic in the 15th century was the same as the Chinese style and definitely nothing like the Western technique she showed in this manga. The Chinese used the Nine-Nine multiplication method which relies on the use of a 9x9 multiplication table and direct addition of multiplication results in decimal increments. Inverting it to do division is a total pain in the ass requiring multiple lines of calculation. There is an anecdote of Nagao Kagetora (Uesugi Kenshin) calculating the triangular number 55 (the result of adding all the numbers from 1 to 10) by using the median method, and everyone thought this was magic and Kagetora a genius. Shizuku being able to calculate 3 warehouses with only six lines of numbers would not look like arithmetic but utter witchcraft to 16th century Japanese. That suggests to me that the author isn't well-versed enough in history to realize the problems with the weapons catalog.