Ancestors in the 1930 U.S. Federal Census - Part 13

I can't find her anywhere...and believe me, I've looked!

Trientje (ZIGTERMAN) BOS BARSEMA, also known as Catherine or Kate, is the maternal grandmother of my maternal (step) grandfather, Adrian DeVRIES. In other words, she is my step-great-great-grandmother. She was born 9 April 1857 in the Netherlands, probably in the northern Province of Groningen, and immigrated in 1879 with her husband Melle BOS--whom she married 29 November 1877 in Bierum, Groningen, the Netherlands--along with their first child, Gertrude, b. c. 1878. They appear in 1880 in Muskegon, Muskegon Co., Michigan as "John and Kattie Boos," child "Gertha," and her brothers, "Sear and Seca Seterman." They next show up in McBain, Missaukee Co., Michigan, where their second child, Johanna "Josephine" BOS, was born in 1885 (the seven-year gap between children makes me suspect there were some miscarriages or infant deaths between Gertrude and Josephine). Before Melle died c. 1888, they had one more child, Melle "Millard" BOS, born 17 July 1887 in Ottawa County. Millard anglicized his surname to BUSH. The family had relatives in Ottawa County; Coopersville is where Millard and Trientje's two brothers settled: Siert or Zigert (also known as Silas) ZIGTERMAN and R. (Sikke) SICHTERMAN.

On 16 October 1889, Trientje married Pieter BARSEMA in Lamont, Ottawa Co., Michigan. Pieter was born 14 March 1854, and his birthplace is also believed to be in the Province of Groningen. He immigrated in 1873 from Eenrum, Groningen, the Netherlands to Grand Rapids, Kent Co., Michigan. At the time of his marriage to Trientje, he was a laborer in Muskegon, Muskegon Co., Michigan. Together, Pieter and Trientje had four children: Nellie (b. c. 1891), Sena C. (b. 26 March 1893), Jennie (b. 28 November 1895), and Peter, Jr. (b. 11 Aug 1898).

By 1927, Trientje, then known as Kate, was living with her son Peter and daughter-in-law Elsie at 1149 "E" Avenue, S.W. in Grand Rapids, and was widowed again. In 1929, I have a residence in Grand Rapids for her, but the next record I have is her certificate for her death on 28 January 1935, which states her residence was Livingston Boulevard, Rural Route 4, Grand Rapids Township, the home of her son, Peter.

So where was she when the 1930 U.S. Federal Census was being taken? I have no idea! I have looked at all of her children's 1930 census records, and can find every one of them, except Peter. Kate is not living with any of her other children during that census, or her brothers, for that matter. I've done all kinds of interesting searches, too: surname, first name, wild card, soundex, birth year, etc. Still no luck. Did their household get skipped? Were they moving? Were they gone for the day? Don't you just hate it when you can't find an ancestor on a census? :-)