It appears that Forest was married first in 1936 (he was 18, his bride was 15). See attached document.
Your query asks "Where does this Bowers name come from on Edith." I found a match in the CA Death Index. The index entry indicates that her married name at the time of her death (July 3, 1948) was Edith E. BOWER, and that her father's surname was WALKER and her mother's surname was JENNINGS. Her burial is recorded at findagrave, with the additional information that her father was Albert David WALKER, and mother Sylvia WALKER. I found a little more information about Edith's death in a newspaper item (see attached image).
I also found a June 29, 1939, newspaper item (Chariton, IA Herald-Patriot):
WALKER-ANGSTEAD WEDDING RECENTLY
Miss Edith Walker, of Russell, daughter of Mr. and Mrs. Al Walker , and Donald* Angstead, of Chariton, were united in marriage at the Presbyterian manse in Unionville, MO, on Monday, June 19, They will make their home in this city.
[*In various records, I see Forest Donovan referred to as "Donald."]
On November 26, 1940, another Herald-Patriot news item read:
Yocom Hospital Notes
Mr. and Mrs. Don Angstead, of Chariton, are the parents of a baby girl, born Saturday, Nov. 23, weight 7 pounds and 4 ounces, and which has been named Donna Jean. I still see mentions of the ANGSTEADs, including Donna Jean, as late as April 23, 1942.
In December 1942, another news item lists Lucas County (Iowa) men who have been called for induction into the army. Among them is "Forrest Donavan Angstead, Rockford, Ill."
Jan. 13, 1943, Morning Star, Rockford IL
BIRTH RATE IN 1942 SETS NEW 25-YEAR MARK
Rockford's birth rate for 1942 was the highest in the last quarter century and probably in all of the city's history. ...
Male parents of the December arrivals include:
... Forest Angstead, FSA trailer camp, girl; ...
An August 19, 1943, Herald-Patriot item reads, "Mrs. Donald Angstead and two daughters moved last week into the Maude Rickey property, formerly occupied ...
On August 24, 1943, a significant item was published in the Rockford newspaper. Because of its sensitive nature, I prefer not to transcribe it here. You may contact me directly and I can provide you with a pdf of the newspaper (maryfobian [at] comcast [dot] net).
On Feb. 24, 1944, a Herald-Patriot item reads, "Mrs. Edith Angstead and baby daughter arrived home Friday from the University hospital, Iowa City."
On February 8, 1945, an item reads, "Mrs.Edith Angstead and three daughters, Donna Jean, Rosemary and Sheryl, moved Tuesday afternoon into the home of her parents, Mr. and Mrs. A. Walker."
In 1945 a Forest P [middle initial may be a mistake] was listed in the Rockford IL city directory, but no wife is listed with him. In 1944 he was listed as Don, but no wife was listed. Note that it is possible to use the address (626 N. Main) as the search phrase and discover the names of everyone who lived at the same address (which appears to have been an apartment or boarding house).
In 1946, ANGSTEAD's brother Mahlon was listed as Killed in Action (he had been missing since March 16, 1945). The article in the Feb. 28, 1946, news item lists one brother among his survivors: "Donovan Angstead of Rockford, Ill."
In 1946, a December 5 news item reads, "Mrs. Al Walker returned on Tuesday of last week from a two months visit in Livermore, Calif., at the home of her daughters, Mrs. Verlyn Wumkes and Mrs. Edith Bowers. En route home she visited in Omaha at the home of another daughter, Mrs. Leo O'Brien, and was accompanied home by her grandchildren, Connie and Leo O'Brien.
Have you discovered any more information about your birth mother since you posted your query in 2014?