Si la sopa queda demasiado fuerte, mi madre añade un poco de agua y sigue removiéndola con calma.

Here quedar does not mean to stay. It often means to turn out, to end up, or to be left in a certain state.

So la sopa queda demasiado fuerte means something like:

• the soup turns out too strong
• the soup ends up too strong

If you used estar, you would simply describe its current state: the soup is too strong.
With quedar, there is more of an idea of the result.

After si for real, possible conditions in the present or future, Spanish normally uses the present indicative:

• Si llueve, no salimos.
• Si la sopa queda demasiado fuerte, mi madre añade agua.

This is the normal pattern for a likely or general condition.

You would not use the subjunctive here. The sentence is talking about a real possibility or a habitual result, not a wish or doubt.

With food and drink, fuerte often means strong, intense, or too powerful in flavour.

For soup, it could mean:

• too concentrated
• too salty
• too strongly flavoured

It does not necessarily mean spicy. For spicy, Spanish usually uses picante.

So demasiado fuerte is best understood as too strong/rich/intense.

Muy fuerte means very strong.
Demasiado fuerte means too strong.

That too idea matters, because the next part of the sentence shows a correction:

• the soup is too strong
• so she adds some water

So demasiado fits the logic better than muy.

The verb is añadir = to add.

In the present tense:

• yo añado
• tú añades
• él/ella añade

The accent mark is part of the normal spelling of the verb form añade. It also helps show the stress: a-ÑA-de.

Do not confuse the ñ with n. They are different letters:

• ano and año are completely different words

So both the ñ and the accent mark matter.

Yes. In everyday Spanish, especially in cooking contexts, echar is very common:

• Mi madre echa un poco de agua.

But añadir is also very natural and slightly more precise or recipe-like: to add.

So:

• añadir = to add
• echar = to put in / add

Both work, but añadir sounds especially appropriate in this sentence.

The fixed expression is un poco de + noun:

• un poco de agua
• un poco de sal
• un poco de tiempo

It means a little bit of.

Poco here works as a noun-like quantity expression, so un poco de is the standard form.

You can also say poca agua, but that means little water in a more direct adjective structure:

• Añade poca agua = she adds little water
• Añade un poco de agua = she adds a little water

The version in the sentence is the most natural one.

Seguir + gerundio means to keep doing something or to continue doing something.

So:

• sigue removiéndola = she keeps stirring it / she continues stirring it

This is a very common structure in Spanish:

• sigue hablando = keeps talking
• sigo estudiando = I keep studying
• seguimos esperando = we continue waiting

It focuses on the continuation of the action.

Because object pronouns can be attached to a gerund:

• removiéndola = stirring it

The la refers to la sopa.

With seguir + gerundio, you usually have two correct options:

• sigue removiéndola
• la sigue removiendo

Both mean the same thing.

When the pronoun is attached to the gerund, Spanish often needs an accent mark to keep the normal stress:

• removiendo
• removiéndola

Yes, absolutely.

These are both correct:

• sigue removiéndola
• la sigue removiendo

They mean the same thing. The difference is mainly where the object pronoun goes.

Spanish allows pronouns either:

• attached to the gerund: removiéndola
• before the conjugated verb: la sigue removiendo

Both are common.

In this context, remover means to stir. That is the natural cooking verb for moving a liquid or mixture around with a spoon.

• remover la sopa = to stir the soup

Mezclar means to mix, which is broader. You can mix ingredients together, but when you are talking about the repeated circular motion in a pot, remover is more precise.

So in a cooking situation:

• mezclar = mix
• remover = stir

Con calma means calmly, gently, or without rushing.

It gives the action a softer, more careful tone. In cooking, it suggests she is stirring in a patient, controlled way.

Spanish often prefers expressions like con calma instead of an adverb ending in -mente.
You could say calmadamente, but con calma sounds more natural and everyday.

Most naturally, it sounds habitual or general:

• If the soup turns out too strong, my mother adds a little water and keeps stirring it calmly.

The present tense in both parts often expresses something that she generally does whenever that situation happens.

So it is not necessarily about one single moment. It sounds like a typical way your mother handles the soup.

Because quedar here describes the result or state of the soup.

• la sopa queda demasiado fuerte

The thing that turns out too strong is the soup, so la sopa is the subject, and the verb is singular:

• la sopa queda
• not quedan

That is why the verb agrees with la sopa, not with mi madre.

Yes, it fits Spain Spanish very well. In cooking, remover is very common in Spain for to stir.

In some Latin American varieties, you may also hear revolver in this meaning. But for Spanish from Spain, remover is a very natural choice.

So if you are learning Spanish as used in Spain, this is a good verb to know.