In my experience, in Munster, when saying a person is something it's always "Dochtúir is ea í".
The basic expression "Is Dochtúir í" is almost never used in this case. It tends to be used only in the form
where you emphasise the adjective:
"Is maith an dochtúir í" = She is a good doctor.

Or when fronting:
Is í an Ghaelainn a labhraítear ina dhúthaigh = It is Irish that is spoken in his area.

However you can also use "is ea" when fronting to be a little more emphatic, particularly when you
mean "it's thus" or it is "the case":
Tar éis na hoíche 'thitim is ea 'thánadar chun áit na coinne = It's the case/It's a fact that after night fall is when they came to the place of the meeting.

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The dialect I use is Cork Irish.
Ar sgáth a chéile a mhairid na daoine, lag agus láidir, uasal is íseal

Go raibh maith agat

Just when I think I've mastered the copula, I read a post like this.

Thanks for that An Lon Dubh. You gave me a couple of new things to practice and listen out for.

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Táim ag foghlaim fós. Fáilte roimh gach aon cheartúchán.