Getting "educated" is a lifelong process. It's not too late to educate a mother who has gone astray by believing in non-Islamic superstitions such as some good thing happened because of someone's stepping into the family? Such people whether be MIL or whatever need to be put in place. Don't get too emotional with rishtays. Be realistic and always try to improve yourself and others close to you.
Fun guy I was just about to mention that, that believing someone is lucky for someone and all that is not even Islamic. I cannot believe people still think about all this stuff. Not to forget hurt the other person's feelings using this.