Why does my mom argue with me about almost everything?

It's very possible that the antidepressant is causing the mood change. There are many choices and sometimes doctors must try several antidepressants before they find one that helps without too many negative side effects.
It's possible that she should be checked for dementia, as well, however if this behavior wasn't an issue before the antidepressant, it's quite likely that the drug is the cause. Either way, the doctor needs to know so he or she can help. Please call as soon as possible and let the the doctor know about this change.
Take care,
Carol

That's a tough one. Our aging parents can be downright stubborn and oppositional as they age. Sometimes it is due to mood changes due to various medical or mental conditions, but I doubt the cause would be antidepressants. Your mother may also be in the early stages of dementia. You didn't say what her personality was like before you noticed the changes. Was she mild mannered or a more assertive type? At any rate, I would recommend if at all possible, find a good counselor and get some weekly talk therapy sessions for yourself. This will definitely help you to develop coping skills and a place to release your tension, because she may get worse. Also try to see if she will let you speak to her doctor, but she will need to give her written permission for you or anyone to discuss her private medical info. I feel for you. Take care. Nancy