Hi Bob, I did some more checking and the 1880 US Census lists Ruby Blake age 74 b. @ 1806 VT as a widow.SO IT MAY BE: She married Allen and had kids and then BLAKE.
There is a Ruby Kellogg Blake (1805-1897death certificate on Ancestry.com, but I could not get it to open.It would be interesting if she "informant" were her son or other family member to prove a connection to Henry B. Allen, with whom she is living as his mother in the 1880 US Census. I also found a reference to Ruby Kellogg on the KELLOGG surname on GENFORUM as saying "married Blake?" so that is a clue also.
The father of Ruby Kelloggb. 11 Oct 1805 Ferrisburg, VT is listed as William Kellogg b. 2 Dec 1779 Rutland County, VT and died 1834 and mother Sarah Cousins b. @ 1781-85 VT and died 1834. Since both seem to be listed as died 1834 that may not be correct. Worldconnect and Ancestry and GENFORUM seem to have slightly different dates, but seem to be the same persons: KELLOGG + COUSINS - child: Ruby
So that may help solve your mystery of who the mother of Henry B. Allen is.
another note: Ancestry.com: death certificate for Henry A (note it still looks like B to me) ALLEN b. 27 Mar 1839 Ferrisburg, VT d. 25 Apr 1919 Pittsford, Rutland, VT
mother listed as Ruby BLACK - I think that it should be BLAKE - easy to mix up the two - I did NOT find a Ruby BLACK in any of the forums, but it is still possible spelling.
hope this information will help you sort out things, but it does look like Ruby Kellogg married first an ALLEN and thenBLAKE.