Learn Hardcore French: Elle reste debout pendant la réunion. - She stays standing during the meeting.

debout is an invariable posture word (often described as an adverb or an invariable adjective) used after verbs like être, rester, se tenir. It never changes form for gender or number:

elle est debout, ils sont debout, elles restent debout. By contrast, posture adjectives like assis/assise/assis/assises or couché/couchée do agree: Elle reste assise. Il reste assis.

Why use rester here? How is it different from être debout, se lever, or se tenir debout?

rester debout: to remain standing over a span of time (the idea in this sentence).
être debout: simply to be on one’s feet; neutral state. Elle est debout pendant la réunion is possible but less explicit about the idea of “staying.”
se lever: to stand up/get up (the action of rising): Elle se lève quand la réunion commence.
se tenir debout: to stand upright/hold oneself upright; a bit more formal or physical/postural. Note that se tenir alone also means “to take place” (event): La réunion se tient lundi.

What does the present tense convey here—something happening now or a habit?

Both are possible in French simple present. Elle reste debout pendant la réunion can mean:

happening now (current meeting), or
habitual behavior (what she generally does). To make it clearly habitual, use the plural: Elle reste debout pendant les réunions. To make “now” explicit, add context: En ce moment, elle reste debout pendant la réunion. Avoid être en train de rester, which sounds unnatural.

Can I say pendant que la réunion… instead of pendant la réunion?

Use pendant + noun, but pendant que + subject + verb:

pendant la réunion (correct here).
pendant que la réunion se déroule/a lieu, elle reste debout (grammatical but heavier).

Are there natural alternatives to pendant?

Yes, with slight nuances:

durant la réunion: near-synonym, a bit more formal.
lors de la réunion: “at the time of,” formal/administrative.
au cours de la réunion: “over the course of,” process-focused.
tout au long de la réunion: “throughout the whole meeting.”
For pure durations: pendant deux heures = “for two hours.” Use pour mainly for intended future durations (e.g., Je pars pour deux semaines), not for ongoing facts.

Where can I place pendant la réunion in the sentence?

Natural placements:

Elle reste debout pendant la réunion. (neutral)
Pendant la réunion, elle reste debout. (also neutral) Avoid splitting reste debout: Elle reste pendant la réunion debout is awkward.

Can I move debout to the beginning or the very end?

Best keep debout right after the verb with posture verbs: rester debout, être debout, se tenir debout. Starting with Debout, elle reste… is rhetorical/poetic. Ending with …pendant la réunion, debout is marked and uncommon in everyday speech.

How do I say the opposite (she stays seated)?

Use the agreeing adjective assis/assise:

Feminine: Elle reste assise pendant la réunion.
Masculine: Il reste assis pendant la réunion.

How do I put this in the past or the future?

Past (passé composé): Hier, elle est restée debout pendant la réunion. (rester uses auxiliary être, so the participle agrees: restée with elle, restés with ils, restées with elles.)
Future: Demain, elle restera debout pendant la réunion.

Is réunion the right word for a business meeting?

Yes. une réunion is the standard word for a work/organizational meeting. Avoid un meeting (in French it’s typically a political rally or sports meet). rencontre is a meeting/encounter between people/teams, and rendez-vous is an appointment. Don’t forget the accent in réunion; La Réunion (capitalized) is the French island.

Any pronunciation tips for the whole sentence?

Elle [ɛl]
reste [ʁɛst] (final -e is mute; French uvular r).
debout [dəbu] (final -t silent).
pendant [pɑ̃dɑ̃] (two nasal vowels; final -t silent).
la [la]
réunion [ʁe.y.njɔ̃] (three syllables; ré-u are two distinct vowels; -ion gives [njɔ̃], a palatal [nj] + nasal vowel). No required liaisons in this sentence.

How do I emphasize the entire duration?

Add toute: Elle reste debout pendant toute la réunion. You can also say Elle reste debout tout au long de la réunion to stress “throughout.”