Need to remove 100% of all data from HD then reinstall (FBI, CIA) :)

Thank you all!

@Tonys317 I need some clarification on the complete plan.
--- I hope I’m asking this the right way.

Cleaning your 1TB HDD using diskpart is ok as recommended and you can do that on your computer.
--- But then bring the wiped drive to her house and do the clean install on her computer?
--- You can use Andre Ten’s recommended Clean Install tutorial mention in post #10.
--- I'm not sure what her boot disk mentioned in post #18 consists of or how it was created but is it possible to conduct the clean install on her computer using that boot disk?
--- If she already has Windows 10 on her computer, Microsoft’s digital license is already there.
--- If she doesn’t have Windows 10 on her computer but the intent is to install Windows 10 with her boot disk do it that way.