A few photos from the movies below can be seen on you tube in a video
about Grace Livingston Hill. (The section on silent films can be found in the middle of the video.
approximately 6 minutes and 20 seconds into the video?)

The Mystery of Mary
Released July 31st., 1915
Based on the book The Mystery of Mary by Grace Livingston Hill Lutz

Cast: (character names unknown...)
Lionel Adams
Miss Bonfelt
Tyler Brooke
Frank Currier
Charles Eldridge
Betty Gray
Richard Leslie
Evart Overton
Anders Randolf

The Mystery of Mary @ the Internet Movie Database

The Enchanted Barn
Released January 27th., 1919
Based on the book The Enchanted Barn by Grace Livingston Hill Lutz

(J. Frank Glendon (date unknown) and Bessie Love (around 1920))

Bessie Love (Shirley Hollister)
J. Frank Glendon (Sidney Graham)
Joseph (Joe) Singleton (John Barnard)
William T. Horne (Walter Graham)
Frank Butterworth (George Hollister)
Dorothea Wolbert as Ella Wolbert (Mrs. Hollister)
Darbey A. Walker (Harley Hollister)
Jean Hathaway as Jane Hathaway (Mrs. Walter Graham)
Otto Lederer (unknown)

Click to enlarge

Summary: Shirley Hollister, a stenographer, finds a large unoccupied stone barn in the country which would make a perfect home for her sick mother and younger brothers and sisters who need fresh air. Sidney Graham, the rich young owner, takes an interest in Shirley, and fixes up the barn as a comfortable bungalow. Shirley falls in love with Sidney. Shirley discovers that Sidney and his father are about to be swindled in a mining stock proposition, and she uses her secretarial skills when evidence is taken to convict the swindlers. Shirley is kidnapped and rescued by Sidney, who leaves his society fiancée for Shirley.
The Enchanted Barn @ the Internet Movie Database
AFI Silent Films Catalog - The Enchanted Barn

The Best Man
Released May 4th., 1919
Based on the book The Best Man by Grace Livingston Hill Lutz.

(J. Warren Kerrigan and Lois Wilson (date unknown))

J. Warren Kerrigan (Cyril Gordon)
Lois Wilson (Celia Hathaway)
Gayne Whitman as Alfred Whitman (Jefferson Hathaway)
Frances Raymond (Mrs. Hathaway)
Clyde Benson (George Hayne)
R. D. MacLean (Secret Service chief)
Bert Appling (Brady)
Edwin B. Tilton as Ed Tilton (Holman)
Mary Land (Mrs. Holman)
Fred Montague (Celia's uncle)

Summary: An international gang of crooks, the Holmans, steal a coded paper and send for their London agent John Burnham, to come to New York to decipher it, but Cyril Gordon, a United States Secret Service agent, impersonates Burnham and retrieves the paper. A taxi meant for Burnham takes Gordon to a church where a George Hayne, Burnham's real identity, is to marry Celia Hathaway, who has not seen Hayne in fifteen years. Remembering that he is to "stop at nothing" to save the code, Gordon marries the rich and pretty Celia and leaves with her on a honeymoon train through Pennsylvania, followed by one of the crooks. Celia berates Gordon for blackmailing her into marriage, but is pleasantly surprised by his character. After some adventures escaping from the crooks, they genuinely fall in love. In Washington, the code is delivered and the thieves captured. After Gordon reveals his secret, the couple acknowledges their desire to stay married.
The Best Man @ the Internet Movie Database
AFI Silent Films Catalog - The Best Man

Marriage in Transit
Released on March 29th., 1925
Based on the book The Best Man by Grace Livingston Hill Lutz

(Edmund Lowe and Carole Lombard in Marriage in Transit)

Edmund Lowe (Holden/Cyril Gordon)
Carole Lombard (Celia Hathaway)
Adolph Milar (Haynes)
Frank Beal (Burnham)
Harvey Clark (Aide)
Fred Walton (Valet)
Wade Boteler (Conspirator)
Fred J. Butler(Conspirator)
Byron Douglas (Conspirator)
Fred Becker (Conspirator)
Edward (Eddy) Chandler (Conspirator)

Click to enlarge

Summary: A gang of crooks led by Holden steals a government code, and Cyril Gordon, a Secret Service agent who bears a strong resemblance to the gang leader, is assigned to recover the stolen documents. Cyril successfully impersonates Holden and recovers the papers. He also gets himself a bride when, in the name of Holden, he marries Celia, a beautiful young woman who was about to sacrifice herself in matrimony to the gangster. Cyril discloses his identity to the girl, and they journey together to Washington, where Cyril reports to his superiors. Holden catches up with the newlyweds and traps them in a hotel room, but Cyril outfights Holden and escapes with his new wife. The gang is broken up, and Celia announces to Cyril that she would be honored to continue as his wife.
Marriage in Transit @ the Internet Movie Database
AFI Silent Films Catalog - Marriage in Transit

Crimson Roses
Not released yet
Based on the book Crimson Roses by Grace Livingston Hill

This movie hasn't been made, but there is a script for the movie...Unfortunately there hasn't been any news about this since 2005. For more information visit this website. :) I'll update this when/if I find out more.
Creative Forse's Crimson Roses website

Grace Livingston Hill Lutz @ the Internet Movie Database