Thanks all.
These have been some of the hardest ancestors in my tree to track down. I really appreciate the help!
Responding to the questions/items brought up:
1. Adella listed her father as David Fenton, laborer from Cork on her marriage certificate. In another document, he is listed as Maurice David Fenton. One of her children was named Maurice. Adella is variously spelled Adela, and Della.
2. We're pretty sure she was Catholic (her children definitely were, even though her British husband was not.)
3. She was married in Maine in 1908 (her path once in the US is fairly well documented, it's her Irish birth/parents/family that are the mystery)
4. We're confident her birth was around 1885 plus or minus a year or two.
5. She herself listed Kilworth as her place of birth. Her death certificate shows 'Cammis' Limerick
6. Her sister Margaret Fenton, came to the US in 1912 and listed her address as Chapel Road, Kilworth. Her birth is variously listed in the 1871-1875 range. (came over on the Lusitania btw)
6. Possible siblings or 1/2 siblings:
Mary Josephine b1865
Thomas b1867 (parents Maurice Fenton, Elizabeth Rice)
Elizabeth b1870 (parents Maurice Fenton, Elizabeth Rice)
William b1872 (parents Maurice Fenton, Elizabeth Rice)
Margaret b1875 (lived with Adelle and took care of her kids when Adelle died) **confirmed sibling
Bridget b1877 (parents Maurice Fenton, Elizabeth Rice)
I still haven't found records that convincingly connect Adelle to her parents and place of birth, or to her siblings.