Sometimes a person needs to face their own strength.
Be supportive, even in full view of the those who offend, but do not engage those persons directly about him/her.
Showing support for your friend openly says a great deal, without further confrontation.
I just watched a movie which depicts this perfectly. It is called Griffin And Phoenix. Someone is facing death, and has a meltdown in a public place. The friend didn’t explain anything to anyone, but the hugging and comforting made obvious this person was suffering and needed some room. It is a hard moment displayed well. I think if I had been the friend, in the moment, I would not have handled it as well. I probably would have defended with some passion and confrontation.
Let me say, I admire your loyalty and friendship. This person is fortunate to have your caring.