As a colloquial choice it is fine. But I don't think that it is acceptable because the sentence from the task has the word "you" and the Russian translation also should have the word "ты" / "вы"

Of course.

Ты is the informal/friendly pronoun "you" and вы is the formal/respectful pronoun "you", as well as the plural "you" (implied as "you all", "y'all", "you guys", "all of you", etc).

Unlike many other languages, English doesn't distinguish between formal/informal "you". Therefore, the sentences have exactly the same meaning in English, unless there is evidence that the pronoun refers to a group of people, in which case вы is best translated as "you all". But be aware that when speaking in Russian people will get offended if you don't use the formal pronoun properly.

Видишь is used after ты, which is the singular for "you". Видим is used after вы, which is the plural for "you".

If you got it wrong just because the question didn't specify if the "you" was plural or singular, I wouldn't worry to much about it.

она = she or feminine "it", so the sentence could be translated as "Do you see it?" but not "Do you see she?". However there are many other ways to say "it" (это, он, него, она, оно, этого) so just be aware of that.

Because она only means 'she', but you need to ask 'Do you see HER?', and to say 'her' you have to use её

There is no difference.