What do you think of me handing my sister-in-law a super-glue when she asked for something to fix her hair?
Why would you do something that is going to seriously damage her hair?
I glanced at her and I felt like she needs to learn a lesson.
You shouldn't use glue on yourself, but you already know that! It is not okay to harm someone with something as powerful as superglue.
What if I just told her that she looks shitty and it's not anybody else's problem?
Giving someone superglue to use in their hair is wrong and unacceptable. You should consider how you would feel if someone did treated you the way that you treated your sister-in-law.