Masculine nouns that start with a vowel get a t- prefix after an in the nominative case.
an t-aerfort, an t-ealaíontóir, an t-im, an t-óstán, an t-uisce
Feminine nouns that start with a vowel don't get a t-prefix.
an aeráid, an eilifint, an inchinn, an obair, an ubh.
I'm surprised that she pronounces 'im' in this way, given her pronunciation of 'dinnéar'. I know native speakers from different parts of Munster who make it rhyme with 'thyme'.
Go raibh maith agat. Sometimes I can't hear the difference between 'i' and 'í' at all - in 'siúlaimid', for instance: I always hear it spoken as though there were a fada on the final syllable.