The phrase "diligent help" is correct and can be used in written English.
Example: "I am grateful for your diligent help in completing this project on time."
"The officials and the referee have been diligent in helping protect quarterbacks and it made a difference.
That, plus the admittedly eccentric home schooling I provided, and his diligent practice, helped rewire his brain to a startling degree, and in time we were able to talk again, he returned to writing books, and even his vision improved.
One particularly diligent monitor helped eject a suspected agent provocateur pretending to be an "international observer", and there were cries of relief among both commission members and monitors when all the numbers added up neatly.
Schools should help diligent students move above their parents' relative status.
But he also thought it something that "some diligent observer, if help'd with better microscopes, may in time detect".
The partnership deals, so complex that even a diligent reader cannot help feeling lost but all adding up to fake profits and hidden losses.
His diligent checks could help to save our lives if anything goes wrong on Syrian shores.
If the governments of Italy, Greece, Egypt, Cambodia and the rest put so little store by their heritage that indigenous pothunters could dig it up and sell it off, it is all the more to the credit of foreign buyers — and the diligent archaeologists who helped to find and excavate the artifacts — that they are now preserved and most of them available for study and display.
Whether these most dire assessments are overstated is a matter of debate, and some newer studies have suggested that a combination of government regulation and diligent conservation is helping to stabilize the falloff, at least in some areas.
