i would definitely not do something as drastic as b&b unless i was reaaallly overdue. black cohosh can raise blood pressure, so if she has bp issues, iw ouldnt do that. both cohoshes can hyperstimulate the uterus, causing really painful ctx without much dilation.
my advice to your friend would be to enjoy her last few days! tell her to check in with herself and make sure all is right in her world- is she ready for baby, is her relationship with dp/babydaddy good, is she worried, etc etc. emotional issues can really stall labor. if she wants to help bring labor on, lots of walking and other activity, orgasms and intercourse, and spicy foods can all help. evening primrose oil can be taken orally and inserted vaginally to help ripen the cervix. the cohoshes can be taken homeopathically to help encourage labor as well.
above all, trust in your body! she will have this baby, when her baby is ready.