Pour elle, ce poste est le meilleur.

Pour is used here to mean from her point of view / for her, as in pour moi, pour lui, pour eux.
À elle is possible in French, but it usually:

• Emphasizes possession: C’est son idée à elle (It’s her idea).
• Or contrasts with someone else: C’est à elle, pas à toi (It’s hers, not yours).

In your sentence, we want “for her / in her opinion”, so pour elle is the natural choice, not à elle.

French has different sets of pronouns:

• Indirect object pronoun: lui (for to him / to her)
• Stressed (disjunctive) pronoun: lui (him) and elle (her) after prepositions

After pour, you must use a stressed pronoun. For a woman, that is elle:

• pour lui = for him
• pour elle = for her

So pour elle (not pour lui) is used because we’re talking about a female person and we’re after a preposition.

Poste in this sentence means job / position / role (a professional position):

• un poste de secrétaire – a secretary position
• un poste de directeur – a director role

It can also mean post, station, set in other contexts (e.g. un poste de radio = a radio set), but here, with ce poste est le meilleur, it clearly means a job or position.

Ce, cet, cette, ces all mean this/that but agree with gender and sound:

• ce before a masculine noun starting with a consonant: ce poste, ce livre
• cet before a masculine noun starting with a vowel or silent h: cet homme, cet arbre
• cette before a feminine noun: cette voiture
• ces for plural: ces postes

Since poste is masculine and starts with the consonant p, you must use ce poste.

Meilleur / meilleure must agree in gender and number with the noun it refers to:

• poste is masculine singular → le meilleur
• If the noun were feminine singular, you’d say la meilleure
  
  • Pour elle, cette solution est la meilleure.

So le meilleur is masculine because poste is masculine.

In French, the superlative “the best” is formed with the definite article + meilleur(e)(s):

• C’est le meilleur film. – It’s the best movie.
• C’est la meilleure idée. – It’s the best idea.

Without the article, meilleur usually means better (comparative):

• Ce poste est meilleur. – This position is better (than some other one, implied).
• Ce poste est le meilleur. – This position is the best (of all in the group).

Your sentence uses the superlative, so you need le.

Meilleur is an adjective (it modifies a noun).
Mieux is an adverb (it modifies a verb, adjective, or another adverb).

• With nouns → use meilleur(e)(s):

  • Ce poste est le meilleur. (best position)
  • C’est la meilleure solution.

• With verbs → use mieux:

  • Il travaille mieux maintenant. – He works better now.

Here, you’re talking about a poste (a noun), so you must use the adjective meilleur, not the adverb mieux.

French, like English, can drop the noun when it’s clear from context:

• Ce poste est le meilleur (poste). – This position is the best (position).
• Cette option est la meilleure (option).

Because poste was already mentioned in ce poste, it’s understood and doesn’t need to be repeated.

The comma is stylistically normal but not absolutely mandatory. It marks Pour elle as a detached phrase showing viewpoint:

• Pour elle, ce poste est le meilleur.
• You might also see: Pour elle ce poste est le meilleur.

In everyday writing, the comma is preferred because it makes the sentence clearer and more natural to read.

Yes, Ce poste est le meilleur pour elle is perfectly correct.

Subtle nuance:

• Pour elle, ce poste est le meilleur.

  • Stronger focus on her opinion: In her view, this is the best position.

• Ce poste est le meilleur pour elle.

  • More focus on suitability: This position is the best one for her (it suits her best).

In many contexts, both can work and the difference is small.

Both can often be translated as “according to her”, but there’s a nuance:

• Pour elle

  • Broad: in her eyes, for her personally (emotionally, practically, morally, etc.)
  • Slightly more informal and common in speech.

• Selon elle

  • Closer to “according to her (opinion / statement)”
  • Feels a bit more neutral or report-like, often used when relaying what someone said or thinks:
    
    • Selon elle, ce poste est le meilleur. – According to her, this position is the best.

So Pour elle feels a bit more about her personal point of view or what’s best for her.

Yes, both word orders are correct, but emphasis changes slightly:

• Pour elle, ce poste est le meilleur.

  • Fronting pour elle emphasizes her viewpoint first.

• Ce poste est le meilleur pour elle.

  • Starts with the job; pour elle comes as an explanation of for whom it’s best.

Both are natural; you just choose where you want to put the emphasis.

Yes, Pour elle, c’est le meilleur poste is correct.

Difference in feel:

• Pour elle, ce poste est le meilleur.

  • Slightly more formal / written; more “structured”.

• Pour elle, c’est le meilleur poste.

  • More natural in speech, more casual; using c’est is very common orally.

Meaning is essentially the same: For her, this is the best position.