Learn Spanish (Latin America): Ella lee un libro en la tarde.

No, it is perfectly correct! The infinitive verb for "to read" is leer. Because it is a regular "-er" verb, you drop the "-er" ending to find the stem, which is le-. Then, you add the present tense ending for ella (she), which is -e. Put them together, and you get lee.

How do you pronounce the double "e" in lee?

In Spanish, you pronounce every single vowel. You don't blend the double "e" into an "ee" sound like you would in the English word "see." Instead, you pronounce both letters as short, crisp "eh" sounds right next to each other: "leh-eh."

Could this sentence also mean "She is reading a book in the afternoon"?

Exactly! In Spanish, the simple present tense is very flexible. Depending on the context, ella lee can translate to "she reads" (a general habit) or "she is reading" (an ongoing action). You don't always need a separate "-ing" verb form like you do in English.

I've seen por la tarde before. Is en la tarde the same thing?

Yes, they mean the exact same thing! While por la tarde is heavily used in Spain, en la tarde is the standard and most common way to say "in the afternoon" in Latin America. It is perfectly fine to use either one.