I understand that how you feel, and I also understand a mother's beliefs. While what she's saying is probably superstition, it also comes from a place of love, where she truly does want you to feel better.
Now, while what she said may be superstition, I will also say going to an event like that usually does help depression. Not because of anything mystical - but you're out of the house, you're with people who you care about and care about you, for an evening you don't need to worry about anything outside of the wedding, it is meant to be an event to enjoy. All of these are proven to help with depression, and an event like a wedding definitely can, if you go into them positively and want to have a good time. If you go into them thinking you're going to have a terrible time - well, you probably will. It's what you make of it.
Either way, responding to your mother's good wishes doesn't have to be extremely negative, (and this is coming from a person who's mother was a fundamental christian who tried to drag me to many many things). In this case, personally without knowing you I'd say go to the wedding. Worst case you get free booze and a decent meal. If you really don't want to, then a simple message to your mom that's like "Mom, I truly do appreciate that you're trying to help me, but I'm just not ready for an event like this. How about we do something quieter?". Acknowledge her trying to help, suggest an alternative.
Final thought: Could it be that she wants you to go with her not for your sake, but for hers? Does she need a plus one and she just wants to spend time with you, but maybe doesn't know how to ask?