"I am a woman."
Translation:Is bean mé.
The Irish for "woman" is bean. It is only lenited (changed to bhean) if there is something that causes lenition. For nouns like bean, the main causes of lenition are the singular definite article an, which lenites feminine nouns, and the possessive adjectives mo, do and a (his), and certain prepositions, which lenite both masculine and feminine nouns. (There are a few other things that cause leniton of nouns, but these are the ones you'll encounter in this course).
As none of of these causes of lenition exist in this sentence, bean is not lenited.
because tá and is don't mean the same thing. Is is for saying something exists as a thing ("I am a woman"), while tá is for saying that something has the quality of some adjective ("I am tall"), or currently doing something ("I am walking").
If you know Spanish, think of the difference between ser and estar.