Well firstly, you need to be commended for coming on here and making the attempt to understand your loved one. She is no doubt struggling immensely and it can be terribly isolating to have bipolar when no one around you understands. it can make all the difference to have one person standing behind you.
In terms of your question about how to approach her when she is acting difficult or irrational, it's a tough question to answer but i'll do my best from my perspective. the first thing that is important to understand is that often, we cannot recognize the changes in our behavior as it is happening. The very nature of bipolar is highly irrational. i know for myself when someone tries to tell me i am acting "off," i often get angry because i don't yet recognize myself that i am acting that way. when it is pointed out i feel a rush of emotion- mostly shame over how i'm acting and treating my loved ones, sadness and frustration over my condition, and even some denial thrown in there because it's hard to face yourself and the people who care when your actions or words have been ugly and hurtful.
how you approach your family member is perhaps the most important thing. keep in mind that she is not trying to act that way and she may not be aware. do your best to keep accusations out of your conversation and always use "I" statements. that means that instead of saying, for example, "
you are acting so irrational these days and you have to go see your doctor," try saying, "
I've noticed that you seem edgier lately and it concerns me. How can i help you to get back on track?" Approaching situations like that can help to make the person not feel ashamed and to open up more.
in regards to why she gets mad when she knows that she is manic and/or not acting right, it's important to consider that she may
not recognize that. i become angry when it's pointed out to me because honestly, i feel incredibly embarassed. bipolar symptoms can sneak up on you- one day you feel great and your meds are working and the next, it seems that everything falls apart. unfortunately, that's the disease. don't assume that she does know how she's acting. it sometimes seems like it's the rest of the world that's crazy and that you yourself (as the bipolar person) is the only rational one (as odd as that sounds!). put yourself in her shoes. when her behavior is pointed out, she is feeling a mixture of emotions that may be overwhelming. another good idea to express your concerns is to try doing it in writing. some people respond better to a simple, caring note than a face-to-face confrontation. ask your loved one what might work for her and try different things until something clicks.
you are a great person for wanting to support her. keep it up- she needs someone like you in her life. i hope i was able to shed a little light on this for you. good luck