La meva germana oblida la clau a casa, però avui la recorda.

In Catalan, a possessive like meva usually goes together with the definite article:

• la meva germana = my sister
• el meu cotxe = my car

So unlike English, Catalan normally uses both:

• article + possessive + noun

This is completely normal and very common.

Oblida is the 3rd person singular present tense of oblidar:

• oblidar = to forget
• oblida = he/she forgets

So La meva germana oblida la clau a casa means something like:

• My sister forgets the key at home or, depending on the intended meaning,
• My sister leaves the key at home because she forgets it

Clau means key, and it is a feminine singular noun in Catalan.

That is why it takes:

• la clau = the key

Compare:

• el llibre = the book (masculine)
• la clau = the key (feminine)

This feminine gender is also important later in the sentence, because the pronoun la refers back to clau.

A casa means at home or to/at the house/home, depending on context.

In Catalan, casa often appears without an article in this expression:

• ser a casa = to be at home
• quedar-se a casa = to stay at home
• oblidar alguna cosa a casa = to forget something at home

So a casa is a very common fixed expression, much like English at home.

Però means but.

It connects two contrasting ideas:

• La meva germana oblida la clau a casa = My sister forgets the key at home
• però avui la recorda = but today she remembers it

So però introduces the contrast.

That la is a direct object pronoun meaning it.

It refers back to la clau:

• la clau = the key
• la recorda = she remembers it

Because clau is feminine singular, the pronoun is la.

So:

• recorda la clau = she remembers the key
• la recorda = she remembers it

In Catalan, object pronouns usually come before a conjugated verb.

So:

• la recorda = she remembers it not
• recorda la ❌

This is one of the big differences from English. Catalan works more like Spanish or French here.

Examples:

• La veig = I see her/it
• El tinc = I have it
• La recorda = She remembers it

Recorda is the 3rd person singular present tense of recordar:

• recordar = to remember
• recorda = he/she remembers

So:

• avui la recorda = today she remembers it

Both oblida and recorda match the subject la meva germana, which is she.

Catalan often leaves out subject pronouns when the verb ending already makes the subject clear.

So instead of saying:

• Ella recorda la clau

Catalan often just says:

• Recorda la clau

In this sentence, the subject is already stated at the beginning:

• La meva germana ... però avui la recorda

So adding ella would usually be unnecessary unless you wanted extra emphasis or contrast.

Yes. The first part sounds like a habitual or usual action:

• La meva germana oblida la clau a casa
  = My sister forgets the key at home / My sister tends to forget the key at home

Then the second part adds a contrast for today:

• però avui la recorda
  = but today she remembers it

So the sentence contrasts:

• what usually happens with
• what happens today

By itself, la recorda could theoretically mean:

• remembers her
• remembers it

The pronoun la can refer to a feminine person or a feminine thing.

But in this sentence, the most natural reference is la clau, so it means:

• she remembers it

Context usually tells you what la refers to.

This is very natural in Catalan, just as it is in English.

First, the noun is introduced:

• la clau

Then, once it is already known, Catalan uses a pronoun:

• la

So the structure is:

• My sister forgets the key at home, but today she remembers it

Repeating la clau again would still be possible, but it would sound more repetitive:

• ... però avui recorda la clau

Using la is smoother and more natural.

Yes, it is very normal.

Basic order here is:

• La meva germana = subject
• oblida = verb
• la clau = object
• a casa = place
• però avui = contrast + time
• la recorda = object pronoun + verb

Catalan word order is often similar to English, but pronouns are one important difference:

• English: she remembers it
• Catalan: la recorda

So overall the sentence is straightforward and natural.