A mi madre se le derramó un poco de sopa al servir la cena.

This is very common in Spanish. The sentence uses indirect object doubling:

• a mi madre = names the person
• le = repeats that person as an indirect object pronoun

So a mi madre se le derramó... literally has both:

• to my mother
• to her

In natural English this feels repetitive, but in Spanish it is normal and often preferred, especially when:

• the person is explicitly mentioned
• the speaker wants to highlight who was affected

So le is not optional here in normal usage. It helps make the sentence sound natural and idiomatic.

No. This se is not truly reflexive. It is part of a very common Spanish pattern used for accidents, unintended events, or things that happened to someone.

In this structure:

• se helps present the event as accidental or unintentional
• le marks the person affected
• the thing that was spilled becomes the grammatical subject

So:

• Mi madre derramó sopa sounds more like my mother spilled soup
• A mi madre se le derramó sopa sounds more like my mother accidentally spilled some soup / some soup got spilled on her while she was serving dinner

This structure often reduces the sense of direct blame and focuses on the event.

Because the grammatical subject is un poco de sopa, and the core of that expression is un poco, which is singular.

So the sentence is structured like this:

• subject: un poco de sopa
• verb: se derramó

That is why it is derramó, not derramaron.

Compare:

• Se derramó un poco de sopa. = A little soup spilled.
• Se derramaron las sopas. = The soups spilled.

The subject is un poco de sopa.

That may feel strange to an English speaker, because in English we often make the person the subject:

• My mother spilled some soup

But in this Spanish structure, the thing involved in the accident is the grammatical subject:

• A mi madre se le derramó un poco de sopa
• literally something like To my mother, a little soup spilled

So mi madre is not the subject. She is the affected person.

Because the sentence is not simply stating the action. It is using a special accidental construction.

Compare the nuance:

• Mi madre derramó un poco de sopa.
  Plain statement: My mother spilled a little soup.

• A mi madre se le derramó un poco de sopa.
  Suggests it happened accidentally, perhaps unintentionally, and emphasizes the mishap rather than the person’s responsibility.

Both can be correct, but they do not feel exactly the same.

Al + infinitive is a very common Spanish structure meaning:

• when ...
• while ...
• sometimes upon ...

So:

• al servir la cena = when serving dinner / while serving dinner

It gives the context in which the accident happened.

Other examples:

• Al entrar, saludó a todos. = When he came in, he greeted everyone.
• Al salir, apaga la luz. = When leaving, turn off the light.

Here it means the soup spilled during the act of serving dinner.

It is understood from context that it is mi madre.

Spanish often leaves out subjects when they are clear from the situation. So al servir la cena does not explicitly say she, but the listener naturally understands that the mother was the one serving dinner.

If needed, Spanish could make it more explicit, but usually it is not necessary.

Yes, that literal version helps show the grammar, but it is not how you would normally say it in English.

A more natural English meaning would be something like:

• My mother accidentally spilled a little soup while serving dinner.
• A little soup got spilled by my mother while she was serving dinner.

The literal version is useful for understanding the structure:

• a mi madre = to my mother
• se le derramó = got spilled on her / spilled accidentally
• un poco de sopa = a little soup

Because mi madre here is not the subject of the sentence. It is an indirect object / affected person, and Spanish marks that with a.

So:

• Mi madre derramó... → mi madre is the subject
• A mi madre se le derramó... → mi madre is the person affected by the accidental event

That a is the normal marker for a person in this role.

Derramar means to spill, to pour out, or to let something flow out.

In this sentence, it means some soup was spilled.

It is a very natural verb for liquids or things like:

• soup
• water
• milk
• wine
• sauce

Examples:

• Se derramó el agua. = The water spilled.
• Derramé café en la mesa. = I spilled coffee on the table.

Yes, if the context already makes it clear who le refers to.

• Se le derramó un poco de sopa. = She/He accidentally spilled a little soup.

But if you want to make the person explicit, add:

• A mi madre se le derramó un poco de sopa.

So the full version is useful when:

• you are introducing the person
• you want emphasis
• you want to avoid ambiguity about le

Un poco de sopa means a little soup or some soup, so it limits the amount. It tells us that only a small quantity was spilled.

If you said:

• A mi madre se le derramó sopa...

that is possible, but it sounds less specific and a bit less natural in many contexts. Un poco de sopa gives a clearer, more idiomatic idea: not all the soup, just a small amount.

Yes, Spanish word order is flexible, though some versions sound more natural than others.

This sentence is very natural:

• A mi madre se le derramó un poco de sopa al servir la cena.

You might also hear:

• Se le derramó un poco de sopa a mi madre al servir la cena.

Both are understandable. Putting a mi madre first gives it a little more prominence, as if the speaker is focusing first on who it happened to.

So word order can shift, but the original version is perfectly natural and idiomatic.