In the U. S., military births are recorded along with the general population. The military might record them too but I don't know how to find them in the military.
You can contact the Center for Health Statistics, www.doh.wa.gov/EHSPHL/CHS/cert.htm to find out about how to order a copy of a birth certificate. They might not release it to you if this Mary or Margaret is still alive.
I did find some other information. In 1910 Marie Hintz and her family were living in Seabeck, Kitsap Co., WA.
Julius C F Hintz, head household, b. Germany, 53 yrs old, marr 22 yrs, farmer.
Ida, wife, b. Germany, 50, had given birth to eight children and all alive in 1910.
Powell [Paul], b. WA, 15.
Herman, b. WA, 14.
Marie, b. WA, 10.
Fritz, b. WA, 9.
In 1920 the family was living in Crosby, Kitsap Co., WA.
Julius C. Hintz, head, b. Germany, immigrated 1884, naturalized 1895, 62, general farmer.
Eda [Ida] A., wife, b. Germany, imm and nat same as above, 59.
Paul, b. WA, 24, single, farmer laborer home.
Marie, b. WA, 20, single.
Rudolph, b. WA, 30, single, farm laborer home.
On 7 June 1925 in Vancouver, Clark Co., WA a minister married Harvey E. Hebert of county of Kitsap, Washington and Mary Hintz of Multnomah Co., Oregon. Witnesses=Rita M. Ferguson, Thomas D. McLean. Source: Certificate of Marriage, Washington State Digital Archives. You can print a copy from this web site at no charge.
In 1930 Ida A. Hintz was living in Seattle, King Co., WA.
Louis Jockel, head household.
Paul A. Bradshaw, dau.
Beverly J. Bradshaw, granddau.
Ida A. Hintz, b. Germany, 69, servant/housekeeper private home, widow.
I couldn't find Harvey and Mary in the 1930 Census. Successful Searching!