Adopted 1st cousin match possible secret sibling?

Question

An unknown woman matches:

• me with 1045cM
• my aunt (my father's sister #1) with 1952cM
• one of my 1st cousins (from my father's sister #2) with 998cM.

My father has one other sibling: a brother who has 4 children (all from same parents). No one in his family has done any dna testing.

My question is, this unknown woman comes up (based on the ages of all involved and the cM's) as my 1st cousin--to high cM to be a half-cousin, too low to be my half-sibling, niece to my dad's sister #1 and 1st cousin to my dad's sister #2.

So does that mean my father's brother and his wife (my aunt and uncle who have 4 kids) had a biological child and gave it up for adoption? I have been in touch with this woman and she told me she was given up for adoption as an infant.

Answer 1

One good way to assess the possibilities in situations like this is to use the WATO tool: What Are The Odds. It's designed to compare the probabilities of various placements in a family tree for an unknown relative, based on the CMs shared with people in known position in the tree. There are instructions here.

You don't have to subscribe to use it for a single 'tree' but you do need to remember to save your work to your computer to reload it later.