A) I didn't claim that; and
B) She didn't solve any multi-body equations so far as I can tell. (Two is not considered multi-body.)
The real problem is figuring out the effect of atmospheric drag; and from what I can tell they had data upon which to build their model.
Papers that include statements like:
for small angles x:... aren't real mathematical papers. They're intended to impress the unwashed.sin x = x
cos x = 1
ML/NJ
Since it’s obvious you didn’t read the linked pdf, I’ll leave you to your delusions. Peace.