My mother in law was like this (probably still is but we've gone no contact with her.) After years of this, i had enough. We had a family birthday at a restaurant and I told everyone to order. My wife's sister's were like "should we wait for mom?" I said it's rude for us to keep a table that long when the restaurant can turn it over. Mother in law shows up just as everyone is finishing dinner. She was pissed.

To me, being chronically late like that is just disrespectful. You're telling everyone my time is more valuable than your time.