Translation:My friend has read all these books.
Now that's a question! They are used in different situations. If you want to know when to use them in a wide range of situations, it is quite a lot to ask. I will try to answer anyway :)
прочитала is used in the following cases:
- the action of reading has been successfully carried out to the end. Reading these books was, probably, expected (otherwise you'd make a generic reference with "читала")
- you arrange actions in sequence: after finishing the books, she did something else, and them something else etc. All these actions should use perfectives then.
- you want to how long it took her to finish the books
- you want to say how many times a person read something fully (emphasises the result; if it is not that important to stress that, use "читала").
читала is used in the following cases:
- the action's result is irrelevant or it ended in failure. The fact that the action happened is important, though. Here, a somewhat successful result is implied because "reading" is unlikely to end in failure naturally—you must say it explicitly if it failed (but it works differently for actions that require effort)
- you make a generic or out-of-the-blue reference to such action (maybe an action might not have been expected to take place). It is not tied to a particular point in time. Think of "I have studied many things" vs. "I studied this stuff two days ago". The difference is, in English you cannot make a non-specific reference with a Present Perfect while simultaneously telling when it was (even though "last year", "yesterday" or "two weeks ago" might be rather blurry, if you think about it). In Ukranian—you can.
- the action is said to be simultaneous to some other action ("I read a book while you were asleep")
- you mean an ongoing action ("was reading")
- you mean a repeated action. Or you mean a "potentially" repeatable action (for example, "I already read this book" may mean that you read it once or twice, or many times—not important; you may even say that you happened to read it once, though still from a point of view of a person who might have read it more than once)
- you want to express the duration of the action (note: "How long did you read?" and "How long did it take you to read the book?" are different)
- you want to say this is the action you filled some time with (e.g., "What did you do yesterday?" "I read books")
TL:DR version: for this sentence the following interpretations are most likely:
- Моя подруга прочитала всі ці книги. → My (female) friend has read all these books (Finished them all. It is likely that she was expected to do so, and I am explicitly saying you that she already finished the assignment)
- Моя подруга читала всі ці книги. → My (female) friend has read all these books. (She read them in the past and knows all these books; she is familiar with what's written there. Maybe she finished them all, though it is irrelevant in this context. Probably you need an advice about these books from a person who read them, and I am telling you that my friend did. Maybe you want to buy her a few books as a present, and I inform you that she already read these books)