HIV transmission between two cis women (that is women who were female at birth and who identify as female) is very rare. There is one documented case of HIV being transmitted this way [https://www.cdc.gov/mmwr/preview/mmwrhTml/mm6310a1.htm]. In this case, one partner was HIV+ and not on medications. The couple engaged in oral sex, vulva-to-vulva contact, and sharing of sex toys. They had sex during menstruation and sometimes had “rough sex” where blood was present. It is difficult to tell exactly which sex act transmitted HIV. So the risk of two cis women transmitting HIV is very low but not zero. The most important intervention you could take would be if you have a female partner who is known to have HIV, she should be on treatment.