Learn Hardcore Portuguese (Portugal): Ela é um pouco tímida, mas fala bem quando está entre amigos. - She is a bit shy, but she speaks well when she is among friends.

ser is used for more permanent or characteristic traits (what someone is like).
estar is used for temporary states or conditions (how someone is at a given moment).

Being tímida (shy) is seen as a personality trait, so European Portuguese uses ser:

Ela é tímida. – She is shy (in general, as a person).

If you used Ela está tímida, it would suggest she is unusually shy right now (maybe because of a specific situation), not that she is generally shy.

Why is it tímida and not tímido?

Adjectives in Portuguese agree with the gender and number of the noun or pronoun they describe:

Ela = she (feminine singular)
So the adjective must also be feminine singular: tímida.

Compare:

Ele é tímido. – He is shy.
Ela é tímida. – She is shy.
Eles são tímidos. – They (masc./mixed) are shy.
Elas são tímidas. – They (fem.) are shy.

What does um pouco tímida add compared to just tímida?

Um pouco literally means a little / a bit, so:

Ela é tímida. – She is shy.
Ela é um pouco tímida. – She is a bit shy / a little shy.

It softens the description: she is shy, but not extremely.

Related intensities:

Ela é muito tímida. – She is very shy.
Ela é bastante tímida. – She is quite/pretty shy.
Ela é um bocadinho tímida. – She is a little bit shy (more colloquial, EP).

Why is it um pouco tímida and not um pouco de tímida?

The structure depends on what follows:

Before a noun, you normally say um pouco de:
- um pouco de água – a little (bit of) water
- um pouco de tempo – a little time
Before an adjective, you normally do not use de:
- um pouco tímida – a bit shy
- um pouco cansado – a bit tired

So um pouco tímida (no de) is the correct pattern because tímida is an adjective.

Why do we say fala bem and not fala bom?

In Portuguese:

bem is an adverb = well
bom/boa is an adjective = good

You need an adverb to describe how she speaks:

Ela fala bem. – She speaks well. ✅
Ela fala bom. – She speaks good. ❌ (ungrammatical, same mistake as in English)

Use bom/boa with nouns, not verbs:

Ela tem um bom português. – She has good Portuguese (her Portuguese is good).
O discurso foi bom. – The speech was good.

Can bem go in another place, like ela bem fala?

Normal, neutral word order is:

Ela fala bem. – She speaks well.

You can move bem for emphasis, but it changes tone and is less neutral:

Ela bem fala, quando está entre amigos.
This has a more expressive/colloquial feel, roughly like:
She really does speak (a lot / well) when she’s among friends.

For everyday, neutral speech describing ability, Ela fala bem is what you want.

Why is there no ela in the second part (mas fala bem quando está entre amigos) ?

Portuguese is a pro‑drop language: the subject pronoun can be omitted when it is clear from context or from the verb form.

Here, ela is already established in the first part:

Ela é um pouco tímida, mas fala bem quando está entre amigos.

In the second clause, the subject is still ela, but Portuguese doesn’t need to repeat it:

… mas fala bem … = … but she speaks well … (implied)
… quando está entre amigos. = … when she is among friends. (implied)

You could say mas ela fala bem quando ela está entre amigos, but it sounds heavy and unnatural in normal speech.

Why is it entre amigos and not com amigos? Do they mean the same?

Both are possible, but they have different nuances:

entre amigos = among friends, focusing on her being in a group of friends, surrounded by them.
com amigos = with friends, focusing more on being together with friends.

In this sentence, entre amigos sounds very natural because it suggests:

When the social environment around her is made up of friends (not strangers), she speaks well.

You could say quando está com amigos, and it would be understood and acceptable, but entre amigos is a very common and idiomatic choice here.

Why is it entre amigos and not entre os amigos? What does the article change?

entre amigos = among (some) friends / among friends in general
entre os amigos = among the friends (a specific group known in context)

In the sentence, we are talking about a general situation:

When she’s in a friendly environment, among friends, she speaks well.

If you say entre os amigos, you are pointing to a specific set of friends that both speaker and listener know (for example, her group of old school friends).

Why are both verbs in the present tense? Is this about a general habit?

Yes. Portuguese present simple is used, as in English, for:

current states: Ela é um pouco tímida. – She is a bit shy.
general, habitual actions: fala bem quando está entre amigos. – She speaks well when she is among friends (whenever that situation happens).

So the present tense here describes what is generally true about her, not just something happening at this exact moment.