For what it's worth I've found Myrtle in 1940, still looking for her in previous years. Given the last name of the question asker I suspect she may be a relative?
Myrtle Williams in the 1940 United States Federal Census
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Name: Myrtle Williams
Age: 17
Estimated Birth Year: abt 1923
Gender: Female
Race: White
Birthplace: Texas
Marital Status: Single
Relation to Head of House: Daughter (Child)
Home in 1940: Altus, Jackson, Oklahoma
Map of Home in 1940: View Map
Street: Ave D
House Number: 620
Inferred Residence in 1935: Altus, Jackson, Oklahoma
Residence in 1935: Same Place
Sheet Number: 14A
Father's Birthplace: Missouri
Mother's Birthplace: Arkansas
Attended School or College: No
Highest Grade Completed: Elementary school, 6th grade
Weeks Worked in 1939: 0
Income: 0
Income Other Sources: No
Native Language: English
Veteran: No
Social Security Number: Yes
Usual Occupation: None
Neighbors: View others on page
Household Members:
Name Age
Mattie Williams 53
Albert Williams 18
Myrtle Williams 17
Elmer R Williams 12
Thelma Williams 12
David Williams 28
Guy Holt 24