Hun lader ikke hvem som helst komme ind, fordi låsen på døren er gammel.

Here lader is the present tense of at lade, and it means to let or to allow.

The pattern is:

lade + someone/something + infinitive

So:

• Hun lader ham gå = She lets him go
• Hun lader ikke hvem som helst komme ind = She doesn’t let just anyone come in

So lader is not about physically leaving something somewhere here; it is about permission.

Hvem som helst is a fixed expression meaning anyone at all, just anyone, or whoever depending on context.

In this sentence:

• ikke hvem som helst = not just anyone

It suggests that she is selective about who is allowed in.

This pattern exists with other question words too:

• hvad som helst = anything at all
• hvor som helst = anywhere
• når som helst = anytime

So it is best learned as a set phrase rather than translated word by word.

Because the meaning is different.

• ingen = no one / nobody
• ikke hvem som helst = not just anyone

So:

• Hun lader ingen komme ind = She lets no one in
• Hun lader ikke hvem som helst komme ind = She doesn’t let just anyone in

The second sentence does not mean nobody is allowed in. It means only certain people are allowed in.

Because after at lade, Danish uses the bare infinitive.

So you say:

• Hun lader ham komme ind
• not Hun lader ham at komme ind

This is similar to English:

• She lets him come in
• not She lets him to come in

Other Danish verbs can also take a bare infinitive, especially modal verbs:

• Jeg kan svømme = I can swim
• Du skal gå = You must go

Ind means in or inside, and with komme it forms the common expression komme ind, meaning come in or enter.

So:

• komme = come
• komme ind = come in / enter

Danish often uses these short directional words with verbs:

• gå ud = go out
• komme ind = come in
• tage med = take along

To an English speaker, these often feel like verb particles, similar to come in, go out, let in, and so on.

Because in a Danish main clause, the finite verb normally comes early in the sentence, and ikke usually comes after that finite verb.

So:

• Hun lader ikke ...

This follows the normal Danish main-clause pattern.

A simplified view is:

subject + finite verb + ikke + rest

For example:

• Han kommer ikke i dag
• Vi forstår ikke spørgsmålet

In your sentence, ikke hvem som helst also works together as a meaningful unit: not just anyone.

Because Danish usually adds the definite article to the end of the noun.

So:

• en lås = a lock
• låsen = the lock

and

• en dør = a door
• døren = the door

This is one of the biggest differences from English. Instead of putting the in front, Danish often attaches it as a suffix.

So:

• låsen på døren = the lock on the door

Because på is the natural preposition here for on the door.

So:

• låsen på døren = the lock on the door

English sometimes uses of where Danish uses på, but in this case on the door is also natural in English.

Danish prepositions do not always match English exactly, so it is best to learn common combinations as vocabulary chunks:

• på døren = on the door
• i huset = in the house
• til skolen = to the school

Because låsen is a singular common-gender noun, and predicate adjectives after er agree with the noun.

The adjective gammel changes like this:

• en gammel lås = common gender singular
• et gammelt hus = neuter singular
• gamle døre = plural
• den gamle lås = definite form

In your sentence:

• låsen is singular and common gender
• so the correct form is gammel

That is why you get:

• låsen ... er gammel

Yes. Fordi introduces a subordinate clause, and subordinate clauses do not use normal main-clause V2 word order.

That is why you get:

• fordi låsen på døren er gammel

and not a main-clause order like:

• fordi er låsen på døren gammel ❌

A useful thing to notice is where ikke would go in a subordinate clause. For example:

• Hun siger, at låsen ikke er gammel

In a subordinate clause, ikke usually comes before the finite verb, unlike in a main clause.

So comparing:

• Main clause: Låsen er ikke gammel
• Subordinate clause: ... fordi låsen ikke er gammel

It can do both, depending on context.

Gammel literally means old, but in many real situations it can suggest something is old-fashioned, worn, unreliable, or no longer in good condition.

So here, if the reason she does not let just anyone in is that the lock on the door is old, the idea may be that the lock is not very secure or dependable.

The adjective itself does not explicitly mean broken, but the context can make that implication natural.