Oooh, you have been busy while I have been asleep, Erato. What a wonderful collection of information..... far more than I expected.
I have a theory on the "gb".......
Given that the 1910 census lists "Margaret L", who is only one year older than Barbara E............ and then 1930 there is "Elizabeth" who is only a year older than Barbara.......... I reckon the "gb" stands for "goes by". I have inherited the same from my own parents, who always called me by my middle name!