Avia addit Siciliam quoque pulchram esse, sed se Athenas videre maluisse.

Because Latin very often uses indirect statement instead of a that-clause.

After a verb like addit (adds, goes on to say), English says:

• she adds that Sicily is beautiful
• she adds that she had preferred to see Athens

Latin usually does this with:

• an accusative subject
• plus an infinitive verb

So:

• Siciliam ... esse
• se ... maluisse

both mean the sort of thing English would express with that.

They are accusative because they belong to an indirect statement.

In Siciliam quoque pulchram esse:

• Siciliam is the subject of the infinitive esse
• in Latin indirect statement, that subject goes into the accusative
• pulchram agrees with Siciliam, so it is also accusative feminine singular

So the pattern is:

• Siciliam = the thing said to be beautiful
• pulchram = describing Siciliam
• esse = to be

Esse is the infinitive to be.

Latin needs it because pulchram is a predicate adjective: Sicily is being described as beautiful. So:

• pulchram esse = to be beautiful

In an indirect statement, Latin uses the infinitive rather than a finite verb, so English that Sicily is beautiful becomes Latin Siciliam pulchram esse.

Quoque means also or too.

It usually comes right after the word it emphasizes. So:

• Siciliam quoque = Sicily too / Sicily also

That suggests Sicily is being added to some previous beautiful place or places already mentioned.

Se is the reflexive pronoun, meaning herself here.

It refers back to the subject of the main verb, which is avia. So:

• avia addit ... se ... maluisse
• the grandmother adds ... that she herself had preferred ...

Latin uses se when the subject of the reported statement is the same person as the subject of the reporting verb.

If Latin used eam instead, that would normally mean her, referring to some other female person, not back to avia.

Maluisse is the perfect active infinitive of malo.

Its principal parts are:

• malo
• malle
• malui

and the perfect infinitive is maluisse.

So maluisse means:

• to have preferred
• or, in smoother English, often just preferred

In this sentence it shows that the preferring happened before the time of addit.

Because malo takes a complementary infinitive.

For example:

• Athenas videre malo = I prefer to see Athens

So in indirect statement:

• se Athenas videre maluisse = that she had preferred to see Athens

Here:

• maluisse = to have preferred
• videre = to see
• Athenas = the object of videre

Because Athens is treated as a plural place-name in Latin.

The forms are:

• nominative: Athenae
• accusative: Athenas

So even though English treats Athens as a single city, Latin uses plural grammatical forms for it.

In this sentence Athenas is accusative because it is the direct object of videre.

Yes.

Sed simply contrasts two things that the grandmother adds:

• Siciliam quoque pulchram esse
• sed se Athenas videre maluisse

So both halves are still governed by addit. The second half does not need another verb like addit repeated, because it is understood.

The important point is relative time.

• addit is present: she adds
• maluisse is perfect infinitive: to have preferred

So the preferring is earlier than the adding.

That is why English often uses:

• she adds that she had preferred to see Athens

Sometimes smoother English may simply say preferred, but grammatically Latin is showing prior action with maluisse.

Because Latin word order is much freer than English word order.

English depends heavily on position. Latin depends much more on endings. That means Latin can separate words that belong together:

• Siciliam ... pulchram esse

even though Siciliam and pulchram go together in sense.

The order here also helps emphasis:

• quoque comes after Siciliam to stress Sicily too
• maluisse comes at the end, giving the contrastive idea a strong finish

So the sentence may look unusual to an English speaker, but its grammar is being shown by forms, not mainly by position.