Hun er alt for træt til at gå ud i aften.

Alt for means far too or much too.

So:

• for træt = too tired
• alt for træt = far too tired / much too tired

The word alt strengthens for here. It does not mean all in this sentence.

Yes. That would still be correct.

The difference is:

• for træt = too tired
• alt for træt = far too tired / much too tired

So alt for adds extra emphasis.

Because træt is the basic singular/common form used with hun.

In this sentence:

• hun = she
• er = is
• træt = tired

You use trætte in some other situations, for example plural:

• De er trætte = They are tired

So here, with one person, træt is correct.

Here til at means something like to in English after an adjective such as too tired to...

So:

• for træt til at gå ud = too tired to go out

This is a very common Danish pattern:

• for + adjective + til at + infinitive

Examples:

• for ung til at køre bil = too young to drive
• for dyrt til at købe = too expensive to buy

Because gå is an infinitive here, and Danish usually uses at before the infinitive in this kind of structure.

• at gå = to go

So:

• til at gå ud = to go out

This is similar to English to go out.

Gå ud is a very common expression meaning go out.

In this sentence, it usually means going out socially, for example to meet people, eat out, go to a bar, and so on.

• gå alone = walk / go
• gå ud = go out

So gå ud i aften means go out tonight, not just walk tonight.

Because it is a prepositional time expression:

• i = in
• aften = evening

Together, i aften means tonight / this evening.

English uses one word, tonight, but Danish expresses the idea differently.

Yes, often it can.

For example:

• Hun er alt for træt til at gå ud i aften.
• I aften er hun alt for træt til at gå ud.

Both are possible, but the emphasis changes a little. Starting with i aften puts more focus on tonight.

Notice that in the second version, er still comes before hun. That is because Danish main clauses follow the verb-second pattern.

Because this is a normal Danish main clause, and Danish usually puts the finite verb in the second position.

So the structure is:

• Hun = subject
• er = finite verb
• the rest of the sentence follows

This is the standard word order for a simple statement:

• Hun er træt
• Jeg kommer i morgen
• Vi går ud senere

Yes.

Er is the present tense of at være = to be.

So:

• jeg er = I am
• du er = you are
• hun er = she is
• de er = they are

Unlike English, Danish uses the same present form er with all persons.

A native speaker would understand it as something like:

She’s far too tired to go out tonight.

The feeling is very natural and idiomatic. It suggests that her tiredness is the reason she will not go out this evening.