"The girl has already seen these countries."
Translation:Девочка уже видела эти страны.
"Увидела" has the meaning of "has just seen", whereas "видела" is used for "has already seen". The same is with "читал(а)/прочитал(а)".
- Ты читал эту книгу? - Да, она очень хорошая. Have you read this book? - Yes, it is very good.
Ты прочитал книгу, которую я тебе дал? - Да, спасибо! Я верну тебе ее завтра. Have you read the book I gave you? - Yes, thank you! I will bring it back tomorrow.
Я видела закат на Чёрном море. - I have seen a sunset on the Black Sea.
- Наконец-то я увидела закат на Чёрном море! - Finally, I have seen a sunset on the Black Sea!
Hope this makes sense.
My Russian teacher said that using the imperfect in sentences like these evolved from a sense of politeness. The perfective usually implies the full completeness of an action. For example, with читать, the perfective means that you have read all of the book from beginning to end, whereas the imperfective just implies that you were in the process of reading it, with no inherent judgment as to whether you finished it or not. So by using the imperfective, you are, in essence, making it easier for the person to say yes and agree for you, by not requiring the person to have completely done whatever you are asking about.