My sister and I recently did DNA tests through 23&Me.
We found out we have a surprise relative about 27 years younger than us (a generation younger). She has about 8.5% shared DNA or around 577 cM's shared with me. She has 10.2% shared DNA with my sister or about 694 cM's.
The crazy thing is that the dnageek website gives it an 81% chance that the relative is my 1st cousin once removed, while it tells my sister the same relative has a 67% chance of being a half niece. So we don't know if she is a 1st cousin once removed or are half niece and thus we don't know if her dad is our dad's kid or our uncle's kid and we can't get any more info.
Any thoughts out there on how to narrow this down from the shared dna data?