There are many ways you could express that there are differences between the two parts of you, the more extreme phase or psychotic phase, and during the times when medication is working. Of utmost importance of course, is that you apologize and try to take responsibility for having said something hurtful. However, as someone who is bipolar and have experienced severe mania, I know how different a person can be during those episodes. You may be able to educate her a little on the things that can happen in the mind of someone who has bipolar, but also to let them know that more and more doctors are discovering that this may be more of a neurological disorder than a psychological disorder. What you say at that specific period of time might have more to do with your insecurity, your own interpretation of something on a subconsious level, or a severe magnification of a character flaw that she does posess. If you tell her of all her strengths that you admire, all the reasons you want to keep her as a friend, and how you have changed since your medications have helped, maybe she will see that she is very important to you, that you do think highly of her, and that you are on the right track to being well. Fear of it happening again may also be part of her not wanting to speak to you, assure her that you will keep a distance in the event one of these events occur, that way she doesnt fear that you will lash out at her again.