"my sister and her friend Samia"
Translation:أُخْتي وَصَديقَتها سامْية
The audio on Duolingo for Arabic is 50% wrong (if not more). Anyway, the ending of the word in Arabic depends on the status of the word and on the articles preceding it sometimes. Sticking to nouns here, the cases are (approximating the Western approach): Nominative, Accusative, and being preceded by a preposition (Dative?). Just to show this by examples:
- Nominative: Her friend Sámiah صديقتُها سامية (cadíqatuhá Sámiyah).
- Accusative: I saw her friend رأيت صديقتَها (ra'aytu cadíqatahá).
- Dative (or whatever): I went to her friend ذهبت إلى صديقتِها (Dahabtu ilá cadíqatihá).
I just like to use "c" instead of "S" for the letter ص. I think it's less ambiguous. Anyway, as you can see here, the ending of the noun (before the possessive article) depends on the status of the word. Duolingo speech machine is not programmed for that. It makes many mistakes grammar-wise as well as spelling-wise. The above examples are the basics, away from the more complex structures that would occur later in depth.
This is why I've written an article a while ago in the main forum of Arabic, advising learners to focus on writing (and reading to some extent) without listening. Individual letters are presumably OK but when it comes to sentences, disasters are awaiting. I guess we can't neglect audio after all even if it is wrong. Besides, from time to time it get stuffed with dialectic expressions and words (e.g. شنطتك instead of حقيبتك for your bag).