Must one make up a full month of Ramadan if she broke her fast due to severe bleeding, knowing that she later discovered she was pregnant with twins and lost one of them, and that her breaking of the fast was based on doctors' advice to avoid worsening the bleeding?

You must make up for the days you missed in Ramadan due to pregnancy or any other reason. As for fasting the days while bleeding, it appears that it is not post-natal bleeding (nifas), due to the possibility of there being two placentas for one fetus, the expelled placenta not remaining, and because blood resulting from a miscarriage of a fetus whose form has not yet been discernible is not considered nifas, but rather irregular bleeding (dam fasad). Fasting in this situation is valid. However, if you wish to make up for these days as a precautionary measure, in agreement with the opinion that a pregnant woman can menstruate, then you may do so, especially if the bleeding coincided with the days of your usual menstrual period.