Her marriage record or her death cert or maybe her obit would be the best places to find her maiden name.
Per the SSDI, a Blanche MATTIER, b 19 Mar 1890 (she was 29 in the 1920 census), d 3 Dec 1972. Her last residence was Dade Co. FL. Try the Miami-Dade County Library first. See http://www.mdpls.org/info/locations/main/gd.asphttp://www.mdpls.org/info/locations/main/gd.asp for more information.
Other sources would be an obit or the death certs of her husbands (Chauncey's would be best) or the birth record or death certs of her children.
The SSDI shows a Clarence F. EWERS, b 2 Feb 1914, d 5 Jan 2003. His last residence was Sylvania, Lucas, OH but there was no obit published in "The Blade", Toledo's newspaper.
A Chauncey Earl EWERS, maybe Earl C. that was about 4 in the 1920 census, died 6 Aug 1988 in Levy Co. FL at age 72.
Harvey MATTIER's obit was in "The Blade" but Blanche was not his mother.