I've sent and email to Border Management Unit and below is the official answer from them. Copying here so maybe it will be helpful for some other people. Long story short, my wife can use EU queue if she is travelling with me :) "Holders of stamp 4 IRP cards are permitted to use the EU queue wh...

Thank you for all the replies. Official answer is very clear.

But I am surprised that non-Irish EU citizens have more rights than Irish citizens in Ireland, ie non-Irish EU citizen's spouse can use EU queue but Irish citizen's spouse cannot

@water_tank1: My wife never had Stamp 4 EUfam. She had Stamp 3 before I was Irish citizen. After my citizenship, she switched to Stamp 4. @Finepaddy: Did sending you back to queue happened in Ireland or any other country? I've just talked to a colleague who is in the same position with me (Irish cit...

Hello, I've checked several pages but couldn't find a relevant answer. I become Irish citizen with the last ceremony at April 2019. After that, we applied to change my wife's stamp and now she has Stamp 4 (not Stamp 4 EUfam). She also has Schengen visa in her passport. Questions: 1) While we travel ...