Learn Portuguese (Portugal): O assistente perguntou se a senhora queria reclamar da fatura. - The assistant asked if the lady wanted to complain about the invoice.

In reported speech, when you are reporting a yes/no question, you use se (if or whether) to connect the reporting verb to the question. The assistant's original direct question was a simple yes/no question: 'Do you want to complain?'.

Why is queria in the imperfect tense instead of the present tense quer?

This happens because the reporting verb perguntou (asked) is in the past tense. When reporting someone's words in the past, a present tense verb from the original direct question shifts a step backward in time, becoming the imperfect tense (queria).

Why is it da fatura instead of using a word for 'about' like sobre?

The verb reclamar (to complain) pairs with the preposition de to indicate what you are complaining about. Since fatura (invoice) is a feminine noun, de combines with the definite article a to become da.

Could a senhora mean 'you' in this context instead of 'the lady'?

Yes! In formal Portuguese, a senhora is used as a polite 'you'. The assistant's original question was likely 'A senhora quer reclamar?' (Do you want to complain?). When reporting it later, it can translate as 'if the lady wanted' or 'if you wanted', depending on who is telling the story.