Mi abuela siempre lleva pantuflas, y mi prima solo se pone el chándal los domingos.

Because llevar and ponerse are related but not identical.

• llevar = to wear / to have on
• ponerse = to put on oneself, and in many contexts also to wear

In this sentence:

• Mi abuela siempre lleva pantuflas suggests a usual state: she always wears slippers.
• Mi prima solo se pone el chándal los domingos focuses more on the act or habit of putting on / wearing the tracksuit only on Sundays.

In everyday Spanish, both verbs can sometimes translate as to wear, but ponerse often feels more like to put on or to choose to wear.

Because ponerse is a reflexive verb when it means to put something on oneself.

• poner = to put
• ponerse = to put on oneself

So:

• pone el libro en la mesa = he/she puts the book on the table
• se pone el chándal = he/she puts on the tracksuit

The se shows that the action is being done to herself.

Spanish often treats clothing a bit differently depending on the verb and the context.

With llevar, it is very common to say:

• lleva gafas
• lleva sombrero
• lleva pantuflas

This sounds natural when talking generally about what someone is wearing.

With ponerse, Spanish very often uses the article:

• se pone el abrigo
• se pone la chaqueta
• se pone el chándal

So both patterns are normal. It is not simply a matter of English a/the.

Pantuflas means slippers.

It refers to soft footwear worn at home. In Spain, learners may also hear expressions like zapatillas de estar por casa, but pantuflas is easy to understand and clearly means slippers.

Chándal means tracksuit.

In Spain, this is a very common word. It usually refers to sporty casual clothes, often a matching sweatshirt/jacket and trousers. In some English varieties, tracksuit is the closest translation; in others, learners might think of sweats or jogging outfit.

In Spanish, article + plural day of the week is commonly used to express a habit.

• los domingos = on Sundays / every Sunday
• los lunes = on Mondays
• los fines de semana = on weekends

So solo se pone el chándal los domingos means she does that as a regular habit on Sundays.

By contrast:

• el domingo usually means on Sunday (one specific Sunday, depending on context)

Here solo means only, and its position helps show what part of the sentence it limits.

• mi prima solo se pone el chándal los domingos = she only wears/puts on the tracksuit on Sundays

This is a natural placement in Spanish.

Be careful: changing the position can change the emphasis.

For example:

• solo se pone el chándal los domingos = the restriction is about the whole action/habit
• se pone solo el chándal = this could suggest she puts on only the tracksuit, and nothing else, which is a different meaning

In modern standard Spanish, solo is usually written without an accent, even when it means only.

Older spelling, or some writers’ personal preference, may use sólo to avoid ambiguity, but the current general recommendation is:

• solo = fine
• sólo = possible in some cases, but usually not necessary

In this sentence, solo is perfectly normal.

No. Mi does not change for masculine vs feminine singular nouns.

So:

• mi abuela = my grandmother
• mi prima = my cousin
• mi abuelo = my grandfather
• mi primo = my cousin

The possessive only changes for number, not for gender:

• mi = singular
• mis = plural

Not necessarily. Here the present tense is being used for habitual actions.

• siempre lleva pantuflas = she always wears slippers
• solo se pone el chándal los domingos = she only wears/puts on the tracksuit on Sundays

So this is the present habitual, which is very common in Spanish, just as in English:

• She always wears...
• She only wears... on Sundays

It describes regular behavior, not just what is happening at this exact moment.