In Alice Munro's "To Reach Japan," what does the paragraph beginning "It’s hard to explain it to anybody now—the life of women at that time. What was okay and what was not" mean in light of Greta's actions? She is a poet: How troubling is the gap between her identities as wife and mother, as poet and artist?

One could argue that the gap between Greta's identity as a poet—or "poetess" as her husband Peter's family insists on calling her—and as a wife and mother isn't really troubling at all. It only seems to be so for those who don't believe that women can be poets as well as wives and mothers.
Greta's referring to a time before the onset of the women's liberation movement, when women weren't expected to read serious books or have ideas of their own. She herself certainly never had any problem with reconciling her roles as writer, wife, and mother. Society, on the other hand, did. That's why Peter's family and his work colleagues put Greta into a little box marked "poetess." This is their way of diminishing Greta and her literary achievements, belittling poetry as a harmless pastime for bored housewives. If they ever started to take Greta and her poetry seriously, then they'd have to challenge their own sexist preconceptions, and that's not something they're prepared to do. In those pre-feminist days being a poetess, with all its patronizing connotations, was considered an acceptable pursuit for a woman; being a poet, however, was not.
https://www.narrativemagazine.com/issues/winter-2012/fiction/reach-japan-alice-munro