Well if you do an Autosomal test that you can either do through Ancestry, 23&Me or FamilyTreeDNA (that's where I my aunt and I took ours) then if I have this right as my Terry being a birth child for my Granduncle then we should match up if she's your mother. That's just an option to trying to narrow down where your mother fits.

If you do a test other than what we have done you can always upload your RAW data to GEDMatch.com to find others who tested elsewhere.

But it will also help you find matches that could lead you to finding your birth mother as well if anyone in that family did a test.

http://blogs.ancestry.com/ancestry/2014/11/13/can-dna-help-y...

Hope this helps. :)