Did I make the correct decision by not meeting my non-Muslim friend after her wedding in the month of Safar, considering that she was a newlywed and the month of Safar is considered inauspicious?
Bismihi ta'ala
There would have been no harm in you congratulating her for her wedding, even though you are in the sacred mourning month of Safar. It is not haram to have done so, as long as you are not intentionally violating the sanctity of the month by engaging in celebrating behaviour, and meeting and congratulating her would not have been such.
And Allah knows best