Marie est vraiment super.

Because the subject is Marie, which is third person singular (she).

The verb être (to be) changes depending on the subject:

• je suis = I am
• tu es = you are
• il / elle est = he / she is

So Marie est means Marie is.

Vraiment means really or truly. It strengthens what comes after it.

So:

• Marie est super = Marie is great.
• Marie est vraiment super = Marie is really great.

In this sentence, vraiment is an adverb modifying super.

In French, adverbs like vraiment usually come before the adjective they modify.

So French says:

• vraiment super

where English says:

• really great

That word order is normal in French.

It is absolutely used in French. Super is very common in everyday speech and means something like great, excellent, or really nice depending on context.

It can feel a bit informal or conversational, but it is extremely common and natural.

Examples:

• C’est super. = That’s great.
• Un film super. = A great movie.

No. Super usually stays the same.

So you can say:

• Marie est super.
• Paul est super.

Unlike many French adjectives, super does not usually add an extra ending for feminine in normal use.

Because super is an adjective, not a noun here.

In Marie est vraiment super, the structure is:

• Marie = subject
• est = verb
• vraiment super = adjective phrase describing Marie

You would not say Marie est une super here, because that would be incomplete and unnatural unless super were part of a longer noun phrase such as une super prof.

A simple approximate pronunciation is:

• est ≈ eh
• vraiment ≈ vray-mahn
• super ≈ soo-pair

A more helpful full approximation:

• Marie est vraiment super ≈ mah-ree eh vray-mahn soo-pair

A few notes:

• The t in est is normally silent.
• In careful speech, there may be a liaison before vraiment, so est vraiment can sound a bit like eh vr..., but learners do not need to force anything unusual here.
• The ending of vraiment is nasal; the n is not fully pronounced like in English.

Not normally. Très super sounds unnatural in standard French.

French usually uses:

• vraiment super = really great
• très bien = very good
• géniale / génial = great, brilliant

So vraiment super is the natural choice here.

It is mostly informal to neutral because of super.

• super is very common in everyday conversation.
• It is not wrong, but in more formal writing you might choose a different adjective, such as:
  • formidable
  • excellent
  • remarquable

So Marie est vraiment super sounds natural and friendly in normal speech.

Yes. Some common alternatives are:

• très = very
  
  • Marie est très gentille.
• tellement = so / so much
  
  • Marie est tellement gentille.
• absolument = absolutely
  
  • Marie est absolument formidable.

But with super, vraiment is one of the most natural choices.

Because Marie already names the subject.

French, like English, usually does not use both a noun and a subject pronoun unless there is a special reason for emphasis or clarification.

So:

• Marie est vraiment super. = Marie is really great.

You would not normally say:

• Marie elle est vraiment super.

That version can exist in spoken French for emphasis, but it is not the neutral basic form.