The listed size is standard length, i.e. the length from tip of the snout to the base of the tail. Based on your picture I'd say your female has a SL of about 4.5".
Common BN are sold in huge numbers. Many are bred, but still loads are wildcaught. Over here basically any BN that is brown with lighter spots will be sold as "common BN". At my LFS batches of wildcaught common BN always contain several species. Only very few people would be willig to pay a lot for a fish that looks like one that you can get for next to nothing everywhere:
So no-one bothers with an ID for these fish. That is why many Ancistrus species are not commercially available. Unless you buy from a very dedicated (cat)fish shop you will not be able to get information on capture location which would be needed to have a chance to get a more accurate ID.
So I am sorry but I do not think that you will get any further than "Ancistrus".