U.S. 1910 Census 'stray'?

I have written before about the Antrim family who emigrated to Jamestown, Pennsylvania possibly in the 1850s. This was not to the original Jamestown colony in Virginia which now is an archeological and heritage site, but to the Jamestown in north-west Pennsylvania on the border of Ohio State. I have now come across an entry in the 1910 US Census which may well add a couple of generations to the family tree which began in Newtoncromelin and Lisnacrogher and Limavallaghan, County Antrim, Ireland.

The entry is for a woman with the odd variation of our surname, Hanna Mcelhaegg, a widow. She was born in Ohio in 1870 and in 1910 was living with her daughter and son-in-law and grandson in New Castle Ward 2, Lawrence, Pennsylvania. She was widowed and the daughter of a father born in Ohio and a mother in Pennsylvania. The family with whom she was living was Hugh and Mavis E. McCain and 11 month old Eugene R. McCain. Hugh was 28 and Mavis 18. McElhaegg had to have been Hanna's married name, and hence Mavis's surname. Who was Hanna's husband, who we assume had died before 1910? There is only one male of the clan who was of her generation, namely William B. McElhager, son of James an Eliza (?nee Rogers). James and Eliza had three daughters, one of whom. Sarah, married a James Eugene Wertman. The repetition of the unusual name Eugene for the McCain's baby surely indicates a family connection. He would have been named after his great-uncle by marriage. It is also possible that his second name 'R' was Rogers, for his great-grandmother. This Census record is the only evidence I have that William B. might have been married. It is also possible that Mavis's second name 'E' might have been Ella, one of the sisters of her father.