doing the right thing!

Me and one of my best friends work at the same place and we are dealing with vendors on different projects. Yesterday she sent an aggressive email to one of their staff and she copied his manager in the email as well.

The manager called me because I am the official point of contact for them and my friend is dealing with them for certain cases only and he told me about the whole incident.

It was the first time to receive a complaint about someone in my level I don't have the privileges to take any action and she is my friend.

I told him for the next time please escalate it to my manager because I can't do anything. 

After that I was thinking should I tell her so she doesn't do the same thing again.

the problem is she doesn't accept advises and take it personally and then a bigger thing will happen that might affect our friendship.

I chose not to talk about it and act like I didn't know anything! sometimes we have to look at a situation from different perspectives and take wrong decisions because the right decision wont work as it should.