Learn Portuguese (Portugal): Ela fez as malas em dez minutos.

In Portuguese, the common expression for 'to pack' is fazer as malas, which literally translates to 'to make the suitcases'. Because this sentence is in the past tense, the verb fazer is conjugated as fez.

I know fazer means 'to do' or 'to make', but is fez a regular past tense form?

No, fazer is a highly irregular verb in the simple past tense. While regular verbs ending in '-er' usually end in '-eu' for the 'he/she' form, fazer becomes fez. For comparison, 'I did' is eu fiz and 'you did' is tu fizeste.

Why does the Portuguese sentence include as malas (the suitcases) when the English translation just says 'packed'?

In English, 'to pack' can be used on its own as a complete action without mentioning bags. In Portuguese, the set phrase fazer as malas requires the noun. It is the standard way to talk about packing for a trip, even if you are only taking a single bag.

Why do we use the preposition em for 'in ten minutes'?

The preposition em is used to indicate the duration of time it takes to complete an action. Saying em dez minutos tells us that the entire process of packing took her exactly ten minutes from start to finish.