ShiraMazor: nice info!
By the way, I include Grammar sentence correction here to keep the thread short.
"lakinna" لَكِنَّ can't be followed directly by its khabar (ie. طيبة Tayyiba).
So, it should be:
قهوةُ سيثٍ بيضاءُ لَكنَّها طيبةٌ.
"qahwatu siithin baiDaa-u2 lakinnahaa Tayyibatun" / "qahwa siith baiDaa lakinnahaa Tayyiba".
If we want to put Tayyiba directly, we may use "lakin" لَكِنْ.
قهوةُ سيثٍ بيضاءُ لَكنْ طيبةٌ.
"qahwatu siithin baiDaa-u2 lakin Tayyibatun" / "qahwa siith baiDaa lakin Tayyiba".
Thank you, Away 54. 1. Why mustn't toyyiba follow directly after لكن? 2. The suffix ها means her, doesn't it? How would that be translated here? 3. I would have thought toyyiba was the second khabar (predicate) of قهوة، not a predicate of لكن، which looks to me like a conjunction joining two predicates, no? I'd love to be shown where I've gone wrong.
(1) "Thank you"
You're welcome, KatieC!
(2). "Why mustn't toyyiba follow directly after لكن?"
"lakinna" (لكنَّ) is a sister of kaana كان that should have 2al-mubtada2 (المبتدأ) and 2al-khabar (الخبر), it is ترفع المبتدأ وتنصب الخبر. So, we cannot put the Tayyiba طيبةٌ directly because "lakinna" لَكنَّ tarfa3 2al-mubtada2 (المبتدع), ie. "haa" ها, and not tarfa3 the verb.
(3) "The suffix ها means her, doesn't it? How would that be translated here?"
Here "haa" ها means "it" and is back to "qahwa" قهوة. The literal translation is "but it is good".
Tayyiba طيبةٌ is the khabar of "lakinna" لَكنَّ. Whilst, the "lakin Tayyiba" لكنْ طيبةٌ (or "lakinnahaa Tayyiba" لكنّها طيبةٌ) phrase is لا محل لها من الإعراب. Or, to make the matter simpler, in short: "Tayyiba is not the second khabar."
Nb: The sentence will be simpler if we use "lakin" لَكنْ. Interestingly, Duolingo spells "lakinna" لكِنَّ as it looks like "lakin" لكِنْ. Possibly, it is a bug from the Course system. Hope they will fix this soon.
Sophia_Eressea, wow thanks a lot for mentioning the term. :)
Here's more about Saxon Genitive: https://www.wallstreetenglish.com/blog/english-possessives-the-saxon-genitive/