By morning sickness, I am assuming that you are referring to the condition of a woman during pregnancy, when she is feeling tired, depressed, and very irritable.
First let me tell you the reason for morning sickness, so that you are better educated about the causes, and that will at least let you know that what is happening to that person is biological and that she is not just angry for no reason. Morning sickness happens in pregnancy because the baby growing inside the mother also needs the nutrients and sugar that the mother eats. When the baby starts taking away some of those resources from the mother, then obviously the mother will suffer from symptoms of low blood sugar etc. And you will also have noticed that 'morning sickness' tends to happen a lot in the morning, and this is because the person hasn't eaten anything for a long time (throughout the whole night while sleeping).
You haven't told me your relationship with the person suffering from morning sickness, so I will just assume it is a close family member. Whatever you do, do not do anything out of the ordinary to anger her. I understand that she is probably overreacting and getting angry at almost every little thing you are doing, but just try to control your own temper and don't be like her, because she can't help it, but you can. Keep in mind that morning sickness will only last until the baby is born. Once that happens, morning sickness is gone.
If you still need more ways to get along with the person, then I can tell you some treatments you can use to help cure morning sickness temporarily from time to time, when it happens. First, don't tell the person go hungry. Make sure they don't have an empty stomach. Instead of making them eat the regular 2 or 3 meals a day, have them eat 5 or 6 smaller meals a day. And these foods are very good for morning sickness: ginger, bananas, apples, and lemons. Tea is also very helpful. And maybe get her to eat dry crackers in the morning, which also help a lot. Also, instead of drinking too much water during meals, have her drink water after about 40 minutes of eating. This is because water dilutes the food while you eat it, which is not good, because then a lot of the nutrients are taken away with the water and are not absorbed in good quantities by the body, which the mother will need to be healthy and in a good mood.
Try those things and I'm sure she will feel better, and in turn, so will you! Good luck.
People develop different habits in their life. These habits may be about eating and drinking, sleeping and rising, dresses of different kinds, roaming about here and there etc. Your question that how do we get along with another person in the family if she has morning sickness, so she is always in a bad mood can be dealt like this.
Earlier I told you that people develop different habits in life and some people are so rigid in their habits that they are not at all ready to change them in any case. Such people I think should be dealt in a soft loving way if you have some problems with their habits. I think that particular girl about whom you are talking in your question is in the habit of sleeping late at night and when she is awoken early in the morning, her sleep is disturbed and she cannot have full required rest and her mood is changed into a bad mood throughout the day. If you have some problem with her, you better try sensibly to make her change her habit of sleeping late so that she could have sound sleep and rise fresh next morning. I think if she manages like this, her problem of morning sickness will be solved and you're as well.