I did a bit of digging today. Herbert John Farrell was born 2 Feb 1894 in Dublin but I can't find a death for him. One possibility in 1951 that might be worth following up when I can get to the library and check the electoral registers.
Also found the probate index for both Dora and Andrew Burrows and both give the same address at 36 West View, Chesham that Agnes was using so that really nails it without even getting certs.
Re: the pension, it wasn't a normal state widows pension - it was specificially for widows of men who had fought in the 1916 Rising. Her husband was awarded it in 1928 but then he died shortly after and the pension died with him.
The legislation to extend it to widows was brought in in 1971 and that's the one she applied for.