Bertha states Frank b Salem, Essex Co MA, so this might be Agnes living in the same county.
1880 Lynn, Essex MA GRANT Wm H 50 NS NS NS [Nova Scotia]; boot maker Mary A 47 NS NS NS Emma J 20 MA Charles H 17 NS Agnes O 12 NS*******[has been afflicted with scrofula for 11yrs......"tumors in the glands of the neck; TB of the lymph glands" She was possibly confined due to this condition; therefore kids placed for adoption????? I didn't find marriage, nor birth records.
Frank is always a boarder on these census; works in shoe factory; age fluctuates 1-2yrs; m at age 19; never middle initial; is consistent with father b MA, mother b ME 1900 Salem, Essex MA; m 14y 1920-30 Brockton, Plymouth MA [1920 widower] Didn't find 1940. His death cert hopefully will name parents. Also can't get a handle on him 1870-80, Every Frank/Francis I found who fits the age, both parents b Ireland.