Are you familiar with the psychologist Paul Ekman's work? He did multicultural research decades ago about facial expressions and found that they were the same throughout the world. Currently he has a website and sells training packages for detecting micro-expressions, expressions that show leakage of emotion, particularly when someone is trying to conceal their feelings.
https://www.paulekman.comShe often has a very angry face when we're discussing something, and if I ask what's wrong she'll deny anything is wrong. I can't convince her I ask because I'm getting a really angry look. I wish I could record her facial expression sometime.
You are obviously reading her feelings and she may be simply unaware or doesn't want to admit to feeling that way. The more you try to "convince" her of what you are perceiving, the more you will elicit her resistance.
And even if you could convince her, it won't lead to any productive change; it's likely to make her even more angry. Better to just trust your own senses and leave it at that.
What does she do when she's angry that makes you want to let her know that you're reading her loud and clear?
