I feel bad for her. They called her mad, but obviously from the few hints you can assume that someone reincarnated into her body and could not adjust to the new environment. Imagine being thrust into some else's body. Unsure of who you are, where you are, if you can get back. Realizing that if you can't, you leave everything and everybody behind. Family, lover, children, keepsakes, and life accomplishments. Having to live your new life and that of an empress with responsibilities to not only a new family but the empire.
Sleeping with a man (the emperor) that is your husband, but also isn't your husband. Taking care of a child that is your child, but that isn't your child. This could be extremely hard especially if you left behind your own loving husband and children. Also you are not actually mad, but they treat you like you're crazy because you are acting like you are a different person because you are indeed a different person, but no one believes you. After the mental wear and tear it's no wonder she gave up in the end.
We so often read stories where the reincarnated person is just like the FL. Always quick to adapt to the situation of being reincarnated, but I honestly feel like alot of us would despair like the empress did. I wonder if she thought ending her life would send her back to where she came from. It also leaves me wondering what happens to the original owner of the body. I wonder if it's safe to assume that the orginal owner and the reincarnated person died at the same time, so when the one soul leaves the other slips in. I hope they address it in the later chapters~