Meine Schwester ist morgens manchmal appetitlos und trinkt nur Tee.

Because Schwester is a feminine noun in German: die Schwester.

The possessive mein- changes its ending to match the noun’s gender, number, and case. Here it is in the nominative singular feminine, so it becomes meine.

• mein Bruder = my brother
• meine Schwester = my sister

The sentence has two coordinated parts joined by und:

• Meine Schwester ist morgens manchmal appetitlos
• (meine Schwester) trinkt nur Tee

In the first part, ist is used with the adjective appetitlos. This works like is hungry / is tired / is loss of appetite in English structure:

• Sie ist müde = She is tired
• Sie ist appetitlos = She is lacking appetite / She has no appetite

In the second part, trinkt is a normal main verb:

• Sie trinkt nur Tee = She only drinks tea

German often leaves out the repeated subject in the second clause when it is obvious, so meine Schwester does not have to be repeated.

Because appetitlos is a predicate adjective, not an adjective directly before a noun.

Compare:

• Sie ist appetitlos → no ending
• eine appetitlose Schwester → adjective ending is required because it comes before the noun

This is a very common pattern in German:

• Der Kaffee ist kalt
• Das Kind ist müde
• Meine Schwester ist appetitlos

Morgens means in the morning(s) or in the mornings.

The -s form is common in adverbial time expressions:

• morgens = in the morning / in the mornings
• abends = in the evening / in the evenings
• nachts = at night
• mittags = at noon / around lunchtime

In this sentence, morgens sounds habitual or general, like in the mornings.

Both can often be translated as in the morning, but there is a nuance:

• morgens often means in the mornings in a general or habitual sense
• am Morgen can refer more to on a particular morning or simply in the morning depending on context

So here:

• Meine Schwester ist morgens manchmal appetitlos
  suggests a repeated pattern: this sometimes happens in the mornings.

German adverb order is flexible, but some placements sound more natural than others.

Here:

• morgens gives the general time frame
• manchmal adds frequency: sometimes

So morgens manchmal means something like sometimes in the mornings.

Other orders may be possible in some contexts, but this version sounds natural and clear. German often organizes information from broader context to more specific detail.

Yes, but the emphasis may change slightly.

For example:

• Meine Schwester ist morgens manchmal appetitlos.
  Neutral: sometimes in the mornings, she has no appetite.

• Meine Schwester ist manchmal morgens appetitlos.
  Also possible, but slightly less smooth for many speakers.

• Manchmal ist meine Schwester morgens appetitlos.
  Stronger emphasis on sometimes.

German word order is flexible, but not random. Moving adverbs often changes what feels emphasized.

Because nur usually goes directly before the word or phrase it limits.

• trinkt nur Tee = drinks only tea

Here, nur limits Tee, so the meaning is that tea is the only thing she drinks in that situation.

Compare:

• Sie trinkt nur Tee = She only drinks tea
• Sie trinkt Tee nur morgens = She drinks tea only in the mornings

The position of nur is important because it changes what only applies to.

Tee is in the accusative case because it is the direct object of trinkt.

• trinken = to drink
• what does she drink? → Tee

In this sentence, Tee looks the same in nominative and accusative because it is a masculine noun with no article here:

• der Tee = nominative
• den Tee = accusative

But since there is no article in the sentence, you just see Tee.

German often leaves out the article with food and drink when speaking generally.

So:

• Sie trinkt Tee = She drinks tea
• Er isst Brot = He eats bread

If you add an article, it becomes more specific:

• Sie trinkt den Tee = She is drinking the tea
• Sie trinkt einen Tee = She is drinking a tea / a cup of tea

Here, nur Tee means only tea in a general sense.

Yes, it is a normal and useful adjective.

It is built from:

• Appetit = appetite
• -los = without, lacking

So appetitlos literally means without appetite.

This -los ending is very common in German:

• arbeitslos = unemployed
• hilflos = helpless
• endlos = endless
• geschmacklos = tasteless / in bad taste

Yes, fairly literally:

• Meine Schwester = my sister
• ist = is
• morgens = in the mornings
• manchmal = sometimes
• appetitlos = without appetite / not hungry / lacking appetite
• und trinkt nur Tee = and drinks only tea

A very literal English version would be:

My sister is sometimes without appetite in the mornings and drinks only tea.

But in natural English, you would usually say something smoother, such as:

My sister sometimes has no appetite in the mornings and only drinks tea.

In a German main clause, the finite verb usually stays in second position.

The first clause is:

• Meine Schwester = position 1
• ist = position 2
• morgens manchmal appetitlos = the rest

German does not count individual words the same way English learners often expect. It counts sentence elements or slots more than raw word count. So even though several words come after ist, the rule is still being followed correctly.

In the second clause after und, the omitted subject is understood, and the verb trinkt comes in the normal finite-verb position for that coordinated clause.