How do I deal with emotional blackmail by my mom?

You walk away emotionally and quite possibly physically as well. Read Boundaries by Townsend and Cloud and learn to set healthy limits on what you allow in your life

What does she have over you? Does she support you? She has control over you solely because you let her. I bet if you really looked at it, she needs you more than you need her.

Your mother has nothing over you unless you allow her to have it. Get therapy from an objective professional who can help you identify healthy boundaries.

I think I am the one here who most says "you need a professional". The fact that you ask this without an example leaves us somewhat up the tree, but the fact is that you DON'T deal with changing others. You deal with your own response. If you are responding from habit know then that most of us do; it is harder to change ourselves than anything else. No matter how painful our path from habitually reacting it is the "known" and the unknown, trying new ways, is so terrifying.
Consider getting help. Your loved one won't change. Mom has likely ALWAYS been this way, and it's working for her. You on the other hand would like to get help. See a professional who has spent a lifetime studying what might work.
A good book to read is the oft recommended Boundaries. It is cheap as anything used on Amazon, and it is full of anecdotes that will help you recognize your Mom and yourself. I am an atheist, and it is quite faith-based, but I must say I liked it a whole lot, and it reads easily, and like entertaining fiction.
Wishing you good luck.

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