The phrase "diligently prepared" is correct and can be used in written English.
It means that something has been carefully and thoroughly prepared with great effort and attention to detail. Example: She impressed her boss with her presentation, which was diligently prepared with hours of research and practice.
Nasser Hussain and Mark Ramprakash battled diligently, prepared to bat with a game plan, and occupy the crease.
It was his younger brother Jeb who held the family's confidence and aspirations, who had diligently prepared for his bid to become governor of Florida in 1994.
While earthquakes that large would be devastating in many parts of the world, the Japanese have diligently prepared for them with stringent building codes and sea walls that are meant to hold back quake-generated tsunamis.
Like a grandmaster positioning his pieces for the first attack, President Obama has diligently prepared the ground for his own entrance into the murky waters of Middle Eastern diplomacy.
Mr. Trump's aides did little to forecast his approach to last night's debate, although in a departure from the lead-up to the Fox News debate last month, he diligently prepared for several days.
Eleven years old at the end of the war, the young Crown Prince diligently prepared himself to become Emperor in the new democratic era, studying English with an American tutor and becoming the first heir to the throne to marry a commoner.
Those who diligently prepare and delay gratification are at the top of the curve.
I know that many of you are diligently preparing for the NPTE exam.
"We've been diligently preparing for anticipated cuts; however, the amount proposed by the governor is excessive".
Diligently preparing for the audition that would change her life, Nina Arianda, 25, ran lines for days, bought new clothes and worked on building her confidence.
When the Centers for Medicare and Medicaid Services first explored a move to ICD-10 more than a decade ago, health insurance plans began diligently preparing.
