I don't think Irene was the same case--Philip's sisters (who would've been prominent, unlike Irene, if they'd been there) had all been married to Germans during the very recent war. Irene's life was very quiet during the war. I would think the case was age and/or ill-health. Irene doesn't seem to have cared about visiting England much after WW1, even though many German royals eventually visited and were received by the royal family.