This might be of interest to you, this is a psychological explanation for you mothers behaviour. If you agree, you can use this to help change her mind on this type of thing.

Here is a simple situation:

A child believes he is smart
He studies for a test and takes the test
When he gets the test he didn’t do well.

He has two choices
1) change his belief. So he is actually dumb
2) lower the relevance of the information. Say the test was too hard, didn’t study enough

this is locus of control. It’s not really related.

Its sort of a little formula::
You have a belief,
You are acquire new information which contradicts the belief
so
You either modify your belief to accommodate the new info. Or you discredit the info and maintain the belief


In your mothers case she is discrediting the information by calling it an opinion.
She is wrong, you know this, I know this, Einstein knows this.

Some people know they do this. But they don’t care, they prefer to keep their incorrect beliefs. I don’t know why it’s probably because they are so attached to them
. It’s sort of a mentality. people ushally call it open or closed minded