Assume that the man making the statement has been married at least twice, and that the woman in question is still alive.
I think that (2) is the way most speakers of English would say it, and it certainly sounds correct, but logically I think that (1) makes a lot more sense.
It isn’t a grammar issue, since both sentences are grammatically correct.
The correct choice is dependent on the situation and on what you are trying to say. “My first wife was Irish” probably has more usages – it indicates that the woman was your wife in the past.
However, in this case – “I’m friendly with my first wife. She is Irish.” – the present tense is better.