I have access to old SD newspapers through genealogybank.com. I see several stories about her horseracing down in Tiajuana, and she is listed as Miss Peggy Childs.
Then there's this story- SD Evening Tribune 11/11/1933
Four Arrested Here As Dope Addicts abstracted Police and Fed agents raided an apartment at 1321 C St. One of the women charged is Peggy Childs, 30, nationally-known woman jockey. Also Joan Baker, 29; Gird Russell, 29; and Kenneth Bausell, 32.
I see stories that say she has a one-horse stable with one horse, Willow Branch.
In a 1929 story, she is referred to as Miss Peggy Childs, from "deah ol' Lunnon".
I saw various postings theorizing that Margaret Childs was born in 1870; that cannot possibly be right, I saw pictures of her taken in the 1930's and she wasn't elderly.
I saw one story that talked about how Willow Branch had been shipped from San Ysidro. San Ysidro is the border crossing town to Mexico. Since I can't find them on censes, I'm thinking that maybe they lived in Tiajuana Mexico.
Times-Picayune, New Orleans, LA 3/10/1929 abstracted Picture- says that she is from London and has only been in the US for 3 months