"Rania is a woman."
If I'm not mistaken the vowel at the beginning of امرأة is much like the on in the definite article ال: It is dropped if there is a word before which ends in a vowel.
Or rather: The lexical entry امرأة isn't actually "imra2a" but rather "mra2a", starting with the م. But Arabic phonology requires a word to start in exactly a consonant and then a vowel. Two consonants in a row at the beginning are not allowed. So if the word which is actually "mra2a" starts a sentence (or otherwise comes after a pause), a helping vowel "i" is inserted before it (along with a pronounced ء so there is a consonant to go with it).* But if there is a word before it which ends in a vowel, that vowel comes before the two consonant in a row so no helping vowel is needed. The same thing happens with ال because, since the noun has to start with a consonant, the "l" will always make it two consonants in a row at the beginning.
There are a handful of other nouns with such a helping vowel in the beginning, including at least two more which are introduced in this course: اِبْن "son" and اِسْم "name".
* In fact the underlying form "mra2a" led to another interesting quirk about امرأة: It has an irregular variation when combined with ال. "The woman" is not اَلْاِمْرَأَة as you would expect. Instead it's اَلْمَرْأَة. What happened is, the first "a" in the underlying "mra2a" swapped places with the "r" to get rid of the three consonants in a row which you would get if you added "al-" to "mra2a". Thus you have "al-" + "mar2a" now, so there is no need for the helping vowel "i" after ال anymore. The other nouns in this course with a helping vowel don't have this quirk because they dont have a vowel which could be pulled back one position, which means the helping vowel must stay to avoid the three-consonant cluster. So "the son" and "the name" are اَلْاِبْن and اَلْاِسْم just as you would expect.