Speaking to BBC Sport, Kirby said of the decision: "It is something I have been thinking about for over a year. I knew this was going to be my last major tournament. The plan was to retire after the Euros but after speaking to Sarina, I'm not going to make the squad. It was like a dagger to my heart but also a weight off my shoulders all at the same time. It was emotional for both of us but we both respected what each person was saying.
"When I woke up in the morning after telling Sarina, I didn't feel any regret. That's when I knew I'd made the right decision. I've been on this team for a long time, it's not going to be a shock that it was coming to an end. You get to a certain age and there are some really good youngsters that are coming through."
In a full statement on social media, Kirby added: "I didn’t ever want this day to come, but I cannot tell you how proud I am it happened. It’s been the biggest honour to represent my country, one that I had only dreamt about as a young girl. I’ve played with incredible players, worked with some incredible managers, played in some amazing tournaments and have some irreplaceable memories."