Emer's house is really nice and perfectly clean. It is a bit hard to find by navigation, but Emer answers very fast and helps you with that.
Emer is a friendly host and the breakfast she offers is really good, fresh and special with lots of self-made things.
The location in Howth is also very good. You can do some nice little walking tours, visit the harbor and it is also pretty easy to reach the airport from here, especially when you are using a rental car.
Due to a badly placed steet-lamp, the room won't be in perfect dark during the evening, but if you don't require that to sleep, I would totally recommend staying at Emer's place.