I'm looking for information regarding by great great grandfather Walter F. MULLEN and his mysterious wife Delia (maiden name unknown, though family lore remembers it as CLANCY)

According to what I know, Walter (born US 1868, died 1928, son of Elizabeth MULLEN) and Delia (alternate for Bridget) (born Scotland? 1869?), were married in Brooklyn in July 1889. They had six children:

Lillian MULLEN b. 1889 (married MCSWIGGAN)
Walter F MULLEN b. 1891
Irene MULLEN b. 1892? (married LAWLOR)
Stephen D MULLEN b. 1894
Alice MULLEN b. 1895 (married EHLERS)
Florence MULLEN b. 1897? (married MAYNARD)

Many of the children later spelled the family name as MULLINS.

Delia ran off with another man (George JOHNSON) circa 1898, and Walter filed for divorce which was granted in May 1899. The family lived in Brooklyn for years afterwards.

I can't find any marriage certificates for Walter and Delia online or any birth or christening records for the children online.

What was Delia's maiden name, when did she immigrate, and where did she go?