La meva mare diu que la seva mare era feliç quan veia els nostres dibuixos.

Because Catalan usually combines the definite article with a possessive:

• la meva mare = my mother
• la seva mare = his/her/their mother
• els nostres dibuixos = our drawings

This is normal in Catalan, even though English usually uses just the possessive without the.

Possessives in Catalan agree with the noun being possessed, not with the owner.

Here:

• mare is feminine singular, so you get meva and seva
• dibuixos is masculine plural, so you get nostres

So:

• la meva mare = feminine singular
• la seva mare = feminine singular
• els nostres dibuixos = plural

Seva can be ambiguous on its own. It can mean his, her, its, their, or formal your, depending on context.

In this sentence, the most natural reading is that la seva mare refers back to la meva mare, so it means her mother — in other words, my mother’s mother.

If a speaker wanted to make it extra clear, they could rephrase it.

Because the sentence mixes two time levels:

• La meva mare diu... = My mother says... → present time
• ...que la seva mare era feliç quan veia... = what she says about the past

So the mother is speaking now, but she is talking about a past situation.

Era and veia are imperfect forms. The imperfect is often used for:

• background description
• ongoing states
• repeated or habitual actions in the past

That fits this sentence well:

• era feliç describes a past state
• quan veia els nostres dibuixos suggests something like when she saw / whenever she saw / when she used to see our drawings

If the idea were one single completed event, Catalan would more likely use a different past form.

In Catalan, ser feliç is the usual way to talk about being happy as a state or condition.

• era feliç = she was happy

Estar feliç can exist, but it often sounds more temporary or situational. In this sentence, era feliç is the more natural choice because it describes her emotional state in that past context.

Because Catalan often leaves subject pronouns out when the verb form already makes the subject clear. This is very common.

So Catalan can say:

• La meva mare diu...
• ...era feliç...
• ...veia...

without repeating ella.

You can add the pronoun for emphasis or contrast, but it is not normally necessary.

Que means that and introduces a subordinate clause after diu:

• La meva mare diu que... = My mother says that...

In English, that is often optional. In Catalan, que is usually kept.

Quan means when. It introduces the time clause:

• quan veia els nostres dibuixos = when she saw / whenever she saw our drawings

Because the verb is in the imperfect (veia), the sense can be broader than a single moment. It may suggest a repeated situation.

Some Catalan adjectives have the same form for masculine and feminine in the singular. Feliç is one of them.

So:

• ell era feliç
• ella era feliç

Both use feliç in the singular.

Only the plural changes:

• masculine plural: feliços
• feminine plural: felices

For the same reason as la meva mare: Catalan normally uses the article together with the possessive.

So:

• els nostres dibuixos = our drawings

This structure is standard and very common in Catalan.