I have completed Ingun Black-Briars "gather ingredients" quest but unlike all the other characters I have helped, the amulet of mara gets no response, which means there is a further quest to do or this character is unmarriable despite seeming like an ideal spouse for a Dark Brotherhood listener.

This seems arbitary and made even less sense after hearing her argument with Maven Black-Briar about Inguns alchemy/Mavens petty scheming which ends with the latter stating "Your interests are what I tell them to be, otherwise you will be homeless and bankrupt".

Does anyone know if there is another quest to do or if not, a console command to get around this?

You can't marry a Black Briar

Those interests don't refer to you, they refer to alchemy Maven doesnt like ingun not contributing to her empire, so maven threatens to dump her on the streets or something. Apparently.