Hun opfører sig altid høfligt over for nye kolleger, og derfor virker hun meget pålidelig.

Because at opføre sig is a fixed reflexive verb meaning to behave.

• opføre by itself usually means something else, such as to perform, to put on, or to erect/build
• opføre sig specifically means to behave / to conduct oneself

So:

• Hun opfører sig høfligt = She behaves politely

The sig is required here. It matches the subject:

• jeg opfører mig
• du opfører dig
• han/hun opfører sig
• vi opfører os

Here høfligt is being used adverbially, so it describes how she behaves.

Compare:

• en høflig kvinde = a polite woman
  
  • here høflig is an adjective describing a noun
• Hun opfører sig høfligt = She behaves politely
  
  • here høfligt describes the manner of the action

In Danish, many adverbs are formed with -t from the adjective:

• hurtig → hurtigt
• rolig → roligt
• høflig → høfligt

over for means towards, in relation to, or in dealing with someone.

So:

• høfligt over for nye kolleger = politely towards new colleagues

It is a very common phrase when talking about attitudes or behavior toward people:

• Hun er venlig over for børn = She is kind to/towards children
• Vær ærlig over for dem = Be honest with them

Because the sentence is talking about new colleagues in general, not one specific colleague or a specific known group.

Form:

• ny kollega = a new colleague
• nye kolleger = new colleagues
• de nye kolleger = the new colleagues

So in this sentence:

• over for nye kolleger = towards new colleagues

Also note that nye has -e because the noun is plural.

That is the normal Danish word order.

In a main clause, Danish usually puts things in roughly this pattern:

subject + finite verb + other verb parts/pronouns + sentence adverb + manner adverbial

So:

• Hun = subject
• opfører = finite verb
• sig = reflexive pronoun
• altid = sentence/frequency adverb
• høfligt = manner adverb

That gives:

• Hun opfører sig altid høfligt

A native English speaker may want to put altid earlier, but Danish word order is stricter here.

Because Danish main clauses follow the verb-second rule (V2).

In the second clause, the first real element is derfor. That means the finite verb must come next:

• derfor virker hun meget pålidelig

Even though the clause starts with og, that og does not count as the first element for V2 word order.

So the structure is:

• og
  • derfor
    • virker
      • hun
        • ...

Not:

• og derfor hun virker ❌

Compare:

• Hun virker meget pålidelig
• Derfor virker hun meget pålidelig

Not here. virke can mean different things depending on context.

1. work / function

• Maskinen virker = The machine works

2. seem / appear / come across as

• Hun virker træt = She seems tired
• Han virker venlig = He seems friendly

In your sentence, it has the second meaning:

• virker hun meget pålidelig = she seems / comes across as very reliable

Because the subject is hun, which refers to a common-gender singular person, so the adjective stays in its basic form:

• Hun virker pålidelig

If the subject were a neuter noun or det, you would use -t:

• Det virker pålideligt = It seems reliable

And in plural:

• De virker pålidelige = They seem reliable

So the form of the adjective agrees with the subject.

meget means very here. It intensifies the adjective pålidelig.

So:

• pålidelig = reliable
• meget pålidelig = very reliable

This is a common pattern in Danish:

• meget venlig = very kind
• meget dygtig = very skilled
• meget interessant = very interesting

Because the sentence contains two main clauses:

1. Hun opfører sig altid høfligt over for nye kolleger
2. derfor virker hun meget pålidelig

In standard Danish writing, a comma is normally used to separate coordinated main clauses, even when they are joined by og.

So the comma helps show the structure clearly:

• first full clause
• og
• second full clause

That is why the sentence is written with:

• ..., og derfor virker hun ...