"اِمْرَأة عَرَبِيّة وَامْرَأة أَمْريكِيّة"
Translation:an Arab woman and an American woman
there are many grammar rules for nunation, depending on sentence structure, simple indefinite sentences (a word and an adjective) is one application of them, but there are others.
In this case both get nunation technically, but in the nunation of the last word is dropped in pronunciation, indicating the end of the sentence. If the sentence continues (like: 'An Arab woman and an American woman...do something) you would hear the nunation in the last word.
To complicate things just a little bit more, this is a taa2 marbootah (a 'tied-up ت'). Which is pronounced as a 't' with casing if applicable (like nunation) if there is a word following it, but pronounced as an 'h' if there is no word following it.
v/s imra2atun 3arabiyyah (an Arab woman)
v/s imra2atun 3arabiyyatun jameelah (a beautiful Arab woman)
v/s imara2tun 3arabiyyatun jameelatun hunaa (a beautiful Arab woman is here)
note how the same word ending changes as the 't' comes in follows by its casing (nunation)
just adding something
The taa2 marbootah (ة or ـة ) is covered inaccurately in the lessons for pronunciation practice.
In the practice lessons its pronunciation is given as an 'aa' which is strictly a Levantine dialect.
Whereas in MSA it is actually a clear 'h' like in 'hat' and the vowel before it almost always a short a ( َ ) or a long aa ( ـا ) which can be detected by looking at the letter before it.
Ofcourse when it is linked with a casing (as in nunation) that 'h' sound changes to a 't' followed by the sound of casing, as in the examples above.
First, a vowel at the start of a word is always carried by ا. That ا may or may not carry a hamza (أ or إ or ا).
If the word starts with a hamza, you pause your voice and then pronounce that vowel, e.g. وَأبي wa-2abii (my father).
If the word starts without hamza, like امرأة in this sentence, you pronounce the vowel only at the start of the sentence or vowelless consonants. Otherwise, you do not pronounce the vowel and just take over the preceding vowel without pausing your voice between the words. وَامْرأَة wa-mra2a