Min veninde skriver altid meget hurtigt, men hun har også det med at glemme et mellemrum efter kommaet.

Veninde specifically means female friend.

• en ven = a friend / a male friend
• en veninde = a female friend

So min veninde tells you that the speaker’s friend is a woman. In everyday Danish, ven can sometimes be used more generally, but veninde is the clear, specific choice here.

Because veninde is a common-gender noun in Danish.

• en veninde
• therefore: min veninde

Danish possessives match the gender and number of the noun, not the person who owns it.

Compare:

• min veninde because veninde takes en
• mit mellemrum would be wrong, but et mellemrum means the noun is neuter, so you say mit with that kind of noun in possessive contexts
• mine venner for plural

So the pattern is:

• min
  • en-word
• mit
  • et-word
• mine
  • plural

Because Danish main clauses normally follow the V2 rule: the finite verb comes in the second position.

Here the structure is:

• Min veninde = first element
• skriver = finite verb in second position
• altid = adverb

So Min veninde skriver altid... is the normal neutral word order.

You can put altid first, but then the verb still has to stay second:

• Altid skriver min veninde meget hurtigt

That is grammatical, but it sounds marked or stylistic. The sentence you were given is the natural everyday version.

Hurtigt is the adverb form of hurtig.

• hurtig = quick, fast
• hurtigt = quickly, fast

So:

• hun er hurtig = she is fast
• hun skriver hurtigt = she writes quickly

The word meget means very here, so meget hurtigt means very quickly.

A useful pattern is:

• meget + adjective/adverb = very + adjective/adverb

So meget hurtigt is completely normal Danish.

Har det med at is an idiomatic expression meaning something like:

• tends to
• has a habit of
• is prone to

So hun har også det med at glemme... means that this is something she often does.

It is not meant to be translated word-for-word. Literally, it looks like has it with to, but that is not how the phrase works in real English or real Danish. Learn it as a chunk:

• have det med at + infinitive

It often suggests a noticeable or slightly annoying habit.

Because at is the Danish infinitive marker, like to in English.

After har det med at, you use:

• have det med at + infinitive

So:

• har det med at glemme
• har det med at komme for sent
• har det med at afbryde folk

This is the standard structure.

Because mellemrum is a neuter noun.

Its basic form is:

• et mellemrum = a space

So the sentence uses et, not en.

In this context, mellemrum means a typing or writing space, not just any kind of physical gap.

Because kommaet is the definite singular form: the comma.

• et komma = a comma
• kommaet = the comma

In Danish, definiteness is often shown by adding an ending to the noun instead of using a separate word like the.

So:

• et komma
• kommaet

In efter kommaet, the idea is after the comma. Danish often uses the definite form in this kind of context.

Yes, it is normal Danish.

Danish can use glemme directly with the thing that was forgotten:

• glemme nøglerne = forget the keys
• glemme et punktum = forget a period/full stop
• glemme et mellemrum = forget a space

English often prefers to describe the action:

• forget to put a space
• forget to add a space

Danish can do that too:

• glemme at sætte et mellemrum efter kommaet

That version is a bit more explicit. The sentence you were given is shorter and very natural.

In a normal Danish main clause, short adverbs such as også, ikke, altid, and tit usually come after the finite verb.

So here:

• hun = subject
• har = finite verb
• også = adverb

That gives:

• hun har også...

This is standard word order.

There can be slight differences in emphasis if you move things around, but hun har også det med at... is the neutral and natural version.

Because men joins two full clauses here, and Danish normally uses a comma before it in that situation.

The two clauses are:

• Min veninde skriver altid meget hurtigt
• men hun har også det med at glemme et mellemrum efter kommaet

So the comma helps separate the two coordinated parts.

It is especially natural here because each side could stand as its own sentence.