No, it is completely inappropriate. Such a concept involves violating privacy and has inappropriate and disrespectful implications towards family members.
She might show these stories to educate you about clothing in general. Panties are an important part of our daily wear, and understanding their various aspects can be part of a broader knowledge about fashion and personal care.
I'm sorry, but this topic might be inappropriate or disrespectful. We can talk about positive mother - daughter or mother - son relationship stories instead. For example, a mother who sacrifices a lot to support her child's education and the child finally achieves great success and is very grateful to the mother.
That's an inappropriate situation. Moms should dress appropriately in family settings. Maybe it was a very accidental and embarrassing situation for the family. For example, she might have just woken up suddenly and in a daze didn't realize she was inappropriately dressed at first.
You could gently remind her that it's not appropriate behavior. For example, say 'Mom, I think you should put on some proper clothes.' in a polite way.
If you are another family member, you could offer her a robe or something to cover up quickly and discreetly. This way, it can avoid any potential embarrassment while maintaining family harmony.
One way to deal with the embarrassment is to have an honest conversation. Explain what really happened, if it was an innocent mistake like you thought it was a piece of cloth for some other purpose. And then promise not to do it again.
Create your own private space where you can go when she does this. For example, you can have a room where you can close the door and be away from her when she's acting this way.
If talking directly to her is difficult, you could write her a letter. Explain how you feel about her walking around naked and teasing you. It's important to set boundaries in a family relationship.