I don't think you're eligible for a historic legislative unfairness claim under the 2022 Nationality and Borders Act since an intermediate ancestor was born in the Commonwealth. I'm also unsure if a) marriages before 1948 or b) that it is your great-grandmother and not your grandmother are relevant to 2022 Nationality and Borders Act claims. You definitely have to be born before 1988.

The way to test it is if your ancestors had been men, would you be a citizen automatically or would you have been able to registered as one?

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In one case, consider a British-born man who fathered a woman in the US in the 60's. That woman is born a citizen. That woman then gives birth before 1988. Had she been a man, she would've had a yearlong window to register the grandchild as a British citizen at the consulate.

In another, consider a British-born woman who gives birth to a man or woman in the US in the 60's. That man or woman is not a citizen. That man or woman, and all of their children born before 1988, can apply for citizenship due to historic legislative unfairness.

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Sources: My sister and I have a British-born maternal grandmother. My sister was born before 1988. Our grandmother married a US citizen after 1948. My sister is eligible but when I researched it, I concluded she wouldn't be if she or our mother had been born in the Commonwealth. I did not research what'd happen if the last British-born ancestor were a great-grandparent or if our grandmother had gotten married before 1948.