The life of Catherine, her parents, and siblings are detailed in the book "The Fowler Family: Early California Pioneers" by Eric Storm (2021).

Catherine Fowler grew up on the frontiers of Illinois and Missouri. In 1846 Catherine traveled in the Harlan-Young Party overland to California with mother (Kitty), sisters (Ann and Minerva), brother (William), husband (John) and 4 young children. She was 25 years old. They took the Hastings Cutoff and were the wagon train just ahead of the Donner Party. Her husband John Hargrave died south of the Great Salt Lake after crossing the Wasatch Mountains. Traveling just a couple weeks ahead of the Donner Party, they were the last party to cross the Sierra Nevada Mountains that year.

In 1847 in California she married George Harlan who had led the wagon train from Missouri. Together they had three children, one of whom died in infancy. They lived some of the time at Hot Springs in the Napa Valley and some in San Francisco. George Harlan died in 1850.

From: Mallett, Fowler. Genealogical Notes and Anecdotes. 1953. p.111
"After the death of George Harlan, Catherine Fowler Harlan, now twice widowed, married Lewis Musgrave, a cousin of her step-father, Calvin Musgrave. They had a son Edward, and two daughters, Ellen Elizabeth and Catherine Florina Musgrave. Edward married Sue Mallott and had a son, named for his grandfather Lewis Musgrave, whose family live in Fresno County. Ellen married Theodore Draper and had three children: Eva, Clarence, and Leo, whose families also live near Fresno. After Theodore Draper died, Ellen was married to Albert Mallott, brother of Edward's wife Sue Mallott Musgrave. Florina Musgrave was married to John Thomas Foley of Oroville, and had two sons and three daughters. …
"After the death of Catherine Fowler Musgrave, her husband Lewis Musgrave remarried and had two children. He engaged in buying and selling livestock, and some years later met with disaster on a horseback trip across Wyoming, where he was erroneously accused of horse stealing. The false charge arose from his falling in with a group of men journeying the same direction, and traveling with them for company. They were the culprits, and getting wind of a posse pursuing them, they scattered and left Lewis Musgrave to face the sheriff's men, though he was wholly ignorant of the crime for which they were sought. Having a clear conscience, he stood his ground when the others galloped off, and when accused asserted his innocence. But the posse would listen to no explanations, and tied him to a bridge timber, then drove his horse from under him leaving him to hang for the crime of which he had no knowledge—a typical miscarriage of lynch law."

[Note: Subsequent research shows the above passage was a sympathetic family remembrance. The newspapers of the time seem convinced of his guilt, and the actions of Musgrave and his colleagues also seem to indicate guilt.]

Father: William Henry Fowler Sr. (b. 1779 in Albany, NY; d. Feb 3 1865 in Calistoga, CA)
Mother: Catherine "Kitty" Speed Fowler Musgrave (b. Sep 24 1801 in Albany, NY; d. May 22 1876 in Napa, CA)

Siblings:
William Henry Fowler Jr. (b. Sep 1817 in Albany, NY; d. Jan 15 1901 in San Ramon, CA)
John Henry Fowler (b. Jun 17 1822 in Belleville, IL; d. Oct 4 1904 in Napa, CA)
Ann Eliza Fowler (Harlan) (b. Jul 4 1830 in Belleville, IL; d. Jun 30 1866 in San Leandro, CA)
Minerva Jane Fowler (Harlan) (b. Mar 3 1833 in Belleville, IL; d. Mar 24 1915 in San Ramon, CA)

Husband (1): John Samuel Hargrave (b. 1819 in AK; d. Aug 12 1846 in UT [first pioneer buried in Utah]). (m. Jun 12, 1836 in MO.)
Children:
1. Mary Jane "Dolly" Hargrave (Swift) (b. May 1835 MO; d. Nov 4 1917 CA)
2. William Hargrave (b. 1838 MO; d. 1848 CA)
3. John Frederick Hargrave (b. Sep 25 1843 MO; d. Apr 2 1923 in Oakland, CA)
4. James Riley Hargrave (b. circa 1845 MO; d. after 1867 CA)

Husband (2): George Harlan (b. Jan 1 1802 in KY; d. Jul 8 1850 in San Jose, CA. (m. fall 1847 in CA)
Children:
1. Sarah Ann Harlan (Farley) (b. Jun 21 1848 San Francisco, CA; d. Mar 10 1923 in Hanford, CA)
2. Jacob Harlan (b. 1849 in CA; d. 1849 in CA)
3. George Harlan III (b. Oct 27 1850 Calistoga, Napa County, CA; d. Jul 10 1874 Kernville, CA)

Husband (3): Lewis H. Musgrave (b. circa 1833 in IL; d. Nov 23 1868 in Denver, CO) (m. May 14, 1856 in Napa County, CA)
Children:
1. Edward Louis Musgrave (b. Feb 11 1857 in Calistoga, Napa Co., CA; d. Mar 29 1937 in Fresno, CA.)
2. Ellen Elizabeth Musgrave (Draper) (b. Dec 1857 in Calistoga, Napa Co., CA; d. Apr 2 1934 in San Jose, CA.)
3. Catherine Florina Musgrave (Foley) (b. Mar 22 1861 in Calistoga, Napa Co., CA; d. Jun 26 1933 in San Francisco, CA.)

1850 United States Federal Census
Nappa Valley, Napa, California, USA
Name: Catherine Harbin [Catherine Harlan]
Age: 30
Birth Year: abt 1820
Birthplace: Illinois
Gender: Female
Family Number: 113
Household Members– Age – Birthplace:
Calvin Musgrave, 31, 9 [step-father]
Catherine Musgrave, 48 [mother]
James C. Musgrave, 9 [half-brother]
Catherine Harbin, 30, [sic Harlan, self]
Sarah Ann Harbin, 3, [sic Harlan]
Mary Jane Hardgrove, 13, [sic Hargrave]
Fredrick Hardgrove, 8, [sic Hargrave]
James Hardgrove, 5, [sic Hargrave]

1860 United States Federal Census
Hot Spring, Napa, California
Family Number: 6
Name: Louis H Musgrave
Age: 27
Birth Year: abt 1833
Gender: Male
Birth Place: Illinois
Household Members – Age – Birthplace:
Louis H Musgrave, 27, Ill
Cathrine Musgrave, 36, "
Edward L Musgrave, 3, Cali
Elen E Musgrave, 2, "
S A Harlow, 12, " [sic Sarah Ann Harlan]
George Harlow, 8, " [sic George Harlan]

Napa County, California, Marriages 1850-1905, Book A, Page 19.
Groom: Lewis H. Musgrave of Fowlers Ranch, Napa Valley, age 23.
Spouse: Mrs. Catherine Harlen [sic] of Fowlers Ranch, Napa Valley, age 34.
Date of marriage: May 14, 1856
Date recorded: June 7, 1856
Married by: James H. McCord, Justice of the Peace

Records of the Families of California Pioneers, 1934, Vol. 4, Page 197, "Family of George Harlan."
Text: Buried in Calistoga at the "Little White Church".
Publication: Daughters of the American Revolution, 1934.
[The old White Church was the first church built in Napa County. Built in 1853, it was situated between St. Helena and Calistoga in what is now Bothe Napa Valley State Park. It was located near the cemetery in which some of the descendants of the Donner Party are buried. The church was named for Asa G. White, a Methodist minister.]