I always wondered if, with Irene, that old "Victorian" rule came into play, where a younger daughter had to be responsible for or to her mother - the "daughter of the house" I think it was termed, where one daughter was guilted into not marrying, & was influenced into staying at home to care for a widowed mother, or her parents.
But Queen Frederika didn't seem to be that kind of mother - she was a pretty independent person and didn't seem to require a daughter in the house. Also, Frederika seemed to be the type of Royalty who wanted her children married off very well
. I suppose THAT could have played a part - maybe when Harald didn't come up to scratch, no lesser man was considered worthy? But even that seems a stretch.
Probably just safer to assume Irene liked an independent life and/or just never met that special someone she wanted to marry. And good for her if that's true. I have a "spinster"
sister and let me tell you, she has a great