I would strongly recommend that you use the BA Terraces lounge in the T1 domestic/Ireland area and not the EI lounge. (I don't believe that BA has a separate first class lounge in this area, unlike in the T1 international area.) The BA lounge is much nicer, and as a OW Emerald travelling on an EI flight operated by EI you have access to the BA lounge for yourself and one guest. The EI lounges are dumps in comparison. It is about a 5 minute walk from the BA lounge to the EI gates.