STRESS AND ANGER!!!!

I decided that I HAVE to be better with my sister,I keep getting SO defensive about her pregnancy, like when she complains about having  Previa, I have not handled it very well. I keep telling her to think positive and that nothing is actually wrong yet, and that she should be happy she is pregers and to think positive. But really, a lot could go wrong...If she had the baby within these next couple of weeks, it would be REALLY bad. Ugh...I feel bad that I have been so bitchy to her, I also hold a lot of grudges towards her from the way she treated me when I m.carried and how she did not seem to care, and still doesn't  AT ALL. She seems to really only care about herself. Now I am having to help out with her baby shower, and I had to help out with her wedding shower too, and all along, she did NOTHING for me for my wedding except show up and do her walk on the cat walk! I am SOOOO frustrated! But I definitely don't want to think "an eye for an eye" you know? Just because she treats me like Appy(my dog) Poop doesn't mean I should treat her that way...it is just SO hard not to say well, you did nothing for my wedding and you treated me like crap during and after my m.carrige and was not there for me AT ALL, so why should I do ANYTHING for you!!! Ahhhhhhhhhhhhhhh!!!! What do I do!?!?!?! I don't want to start trouble, but I definitely feel like crap having to help with her shower, I am having to help out with the invitations and all along I am thinking THIS IS SO UNFAIR!!!! I am definitely not handling the shower planning with a smile on my face, and it is SO obvious!!!