Are you sure it was a sister to Martha and not a brother to John Allen that lived in Little River Co? I find an Alvin T. Allen b 1835 OH in Burke TWP Little River Co AR in 1900 & 1910. In the 1850 Geauga Co OH census I find Alvin T b 1835 as an older brother to John b 1841. They are sons of John b Ireland & Cordelia(Fidelia)b OH.

You have stated Martha King Allen died in 1904. Have you ever checked to see if there is a death certificate on her? What abt the death cert on Lena? That should give where her mother was born anyway, and that could help.

I have searched for a Martha M King b ca 1845 OH with a sister and whose father was b CT , but have not found one.
The King males I find b CT do not have a dtr that fits Martha. Of course, she could be listed by her middle name(Mary, Margaret, etc).

If you have any more clues, let me know and I will see if I can place her with parents in 1860 before she married John Allen in 1866 in Ashtabula Co OH.

Rayedene