mascara
The Spanish word 'rímel' translates to 'mascara' in English. Mascara is a cosmetic commonly used to enhance the eyelashes. It may darken, thicken, lengthen, and/or define the eyelashes. It is usually in a tube with a round brush for applying the product on the lashes. In Spanish speaking countries, the word 'rímel' is often used as a general term for mascara, regardless of brand.
She always carries mascara in her purse.
In this sentence, the speaker is explaining that a particular woman always carries mascara (rímel) with her in her purse. It is common to use 'lleva' to express the action of carrying or having something on one's person in Spanish.
Wearing waterproof mascara is a good idea if you are going to the beach.
Here, the person is recommending using waterproof mascara (rímel a prueba de agua) when planning to go to the beach. The importance of using waterproof makeup products in such scenario is highlighted in the phrase.
Can I lend you my mascara?
In this question, the speaker is offering their mascara (rímel) to someone else. 'Prestar' means to lend, in Spanish, and is used here to denote offering a personal item for someone else's temporary use.