Marie garde ses pantoufles pendant qu’elle prépare le café en tablier.

Yes, garder often means to keep, to keep on, or to look after, but in this sentence it has the idea of keeping something on oneself.

So Marie garde ses pantoufles means something like:

• Marie keeps her slippers on
• more naturally in English: Marie is still wearing her slippers

French sometimes uses garder where English would prefer keep on or simply wear.

Because pantoufles is plural.

In French, possessive adjectives agree with the thing possessed, not with the owner:

• son / sa / ses = his / her / its
• ses is used before a plural noun

So:

• sa pantoufle = her slipper / his slipper / its slipper
• ses pantoufles = her slippers / his slippers / its slippers

Even though Marie is feminine, French does not choose sa or ses based on the owner’s gender here. It chooses ses because pantoufles is plural.

Because the sentence is talking about slippers as a pair, just as English often says slippers.

• une pantoufle = one slipper
• des pantoufles = slippers / a pair of slippers

So ses pantoufles is the normal way to say her slippers.

Pendant que means while.

It introduces something happening at the same time as the main action:

• Marie garde ses pantoufles pendant qu’elle prépare le café.
• Marie keeps her slippers on while she prepares the coffee.

Be careful not to confuse:

• pendant = for / during
• pendant que = while

For example:

• pendant deux heures = for two hours
• pendant que je travaille = while I’m working

This is called elision.

In French, que becomes qu’ before a word that starts with a vowel or a mute h. Since elle starts with a vowel sound, you must write:

• qu’elle

not:

• que elle

This is very common in French:

• qu’il
• qu’on
• qu’elle
• qu’ils

Because after pendant que, you need a conjugated verb, not an infinitive.

Here, the subject is elle, so the verb préparer is conjugated in the present tense:

• je prépare
• tu prépares
• il/elle prépare

So:

• pendant qu’elle prépare le café = while she prepares the coffee

If you used préparer, it would be ungrammatical here.

En tablier means wearing an apron or in an apron.

Here, en is used to describe what someone is wearing, especially in a general or descriptive way.

So the sentence suggests:

• Marie is preparing the coffee
• and she is doing so while wearing an apron

This is a fairly compact French way to express clothing or appearance.

After en in this kind of clothing expression, French often does not use an article.

So you get:

• en tablier = wearing an apron
• en robe = in a dress
• en uniforme = in uniform

This use of en focuses on the person’s appearance or state.

You could say avec un tablier, but that sounds a bit different:

• en tablier = dressed in an apron / wearing an apron
• avec un tablier = with an apron

En tablier is the more natural expression here.

It describes Marie, not the coffee.

So the meaning is:

• Marie prepares the coffee
• and Marie is wearing an apron while doing it

Even though en tablier comes after le café, French speakers understand that it refers to the person doing the action, not to the coffee.

Here le café means the coffee—usually the coffee being prepared in that situation.

French often uses the definite article where English may also use the, especially when the context makes the thing clear.

• préparer le café = prepare the coffee / make the coffee

If you said préparer du café, that would mean more like prepare some coffee.

Both can be possible in other contexts, but préparer le café is very natural when referring to the coffee for that moment, such as the household coffee or the usual coffee being made.

Yes, porter ses pantoufles would also be understandable and natural, because porter means to wear.

But there is a small nuance:

• porter = to wear
• garder = to keep on / to continue wearing

So Marie garde ses pantoufles can suggest that she keeps them on while doing something else. It highlights continuity a little more than porter does.