Le clignotant de la voiture de Marie ne fonctionne plus, alors elle préfère freiner tôt.

Clignotant is the French word for a car’s turn signal, indicator, or blinker. In everyday driving context, all three English terms fit depending on region.

It is a masculine noun, so you say le clignotant.

Le means the, while un means a.

Here, le clignotant refers to a specific indicator: the one on Marie’s car. Since it is identifiable from the context, French naturally uses the definite article le.

French also uses articles a bit more regularly than English, so the indicator of Marie’s car sounds natural in French even where English might phrase things differently.

French usually expresses possession with de:

• la voiture de Marie = Marie’s car
• literally, the car of Marie

English often uses ’s, but standard French normally does not. So instead of Marie’s car, French says la voiture de Marie.

You see de twice in le clignotant de la voiture de Marie because there are two possession links:

• le clignotant de la voiture = the car’s indicator
• la voiture de Marie = Marie’s car

Because voiture is a feminine noun.

After de:

• de + le becomes du
• de + la stays de la

So:

• de le clignotant → du clignotant
• de la voiture stays de la voiture

Since voiture is feminine, de la voiture is correct.

Proper names like Marie, Paul, or Paris usually do not take an article in standard French.

So you say:

• la voiture de Marie not
• la voiture de la Marie

There are some regional or special stylistic exceptions, but in normal standard French, no article is used before Marie here.

Ne ... plus is a negative expression meaning no longer or not anymore.

So:

• fonctionne = works / functions
• ne fonctionne plus = no longer works

The two parts go around the conjugated verb:

• ne
  • fonctionne
    • plus

This is very common in French:

• Je ne sais plus = I don’t know anymore
• Il ne vient plus = He doesn’t come anymore

Not by itself in the usual positive sense. In ne ... plus, the whole expression means no longer / not anymore.

Compare:

• J’en veux plus.
  This can mean I want more of it in a positive context.

• Je n’en veux plus.
  This means I don’t want any more of it / I don’t want it anymore.

So in your sentence, plus is part of the negative structure ne ... plus, not the simple idea of more.

Grammatically, elle could refer to either a feminine noun like la voiture or to Marie, who is female. But context tells you it refers to Marie.

Why?

Because the rest of the sentence says:

• elle préfère freiner tôt

A person can prefer to brake early. A car does not normally prefer anything. So the natural interpretation is that elle refers to Marie.

Because préférer is followed directly by an infinitive.

So you say:

• Elle préfère freiner. = She prefers to brake.

Not:

• Elle préfère de freiner.

Some French verbs do need à or de before another verb, but préférer does not when followed by an infinitive.

Other examples:

• Je préfère attendre. = I prefer to wait.
• Nous préférons partir tôt. = We prefer to leave early.

Freiner means to brake or to slow down by braking. Yes, it is the normal and precise verb here for driving.

It comes from frein, meaning brake.

So:

• freiner tôt = to brake early

That sounds natural in a driving context.

Tôt means early.

So freiner tôt means to brake early, in the sense of starting to brake sooner than usual.

That is different from rapidement, which means quickly.
Compare:

• freiner tôt = start braking earlier
• freiner rapidement = brake quickly

In this sentence, the idea is that since the turn signal is not working anymore, she chooses to begin braking sooner to give other drivers more warning. So tôt is the right word.

Here alors means so, therefore, or as a result.

It links the two ideas:

• the indicator no longer works
• as a result, she prefers to brake early

So alors is acting as a connector showing consequence.

Yes. Both are possible, but there is a slight difference in tone.

• ne fonctionne plus = more neutral or slightly more formal
• ne marche plus = very common and a bit more conversational

For a device like a turn signal, both are natural:

• Le clignotant ne fonctionne plus
• Le clignotant ne marche plus

The sentence you have uses the more neutral fonctionne.