My sister wants to have dinner with her boyfriend's parents. What can she do to lose face?

My sister is going to have dinner with her boyfriend's parents.

In fact, let nature take its course, just be yourself without deliberately doing anything, and be generous and decent.

You can make a good impression on each other.

I heard that the old lady is very arrogant, which is also heard that as long as she touches her face, the other person can understand without being aggressive.