Without a tone of voice to go with the words or more context I would take both of these as meaning the same thing. Though if you want to sound more native when referring to girls around your age you could say "she is very cute" or "she is a very cute girl".

Both are correct but have slightly different nuances. I feel like "She is a very beautiful girl" is kind of just stating a fact, whereas "She is such a beautiful girl" has a stronger nuance, and it often conveys that the speaker feels some way about it, if that makes sense. Some examples: if the speaker wished they could ask the girl out, "Ugh, she's such a beautiful girl, but she lives in another city so that wouldn't work out."; or if the speaker wished they could look like that girl, they might say "Oh, she's such a beautiful girl! I wish I could look like that, even for a day!" Another note would be that when speaking, most of the time, either "such" or the following adjective will be at least a little emphasized/stretched out. Hope this helped :)

The only thing that I want to add is that the reason why these sentences mean basically the same thing is because "such" is an intensifier that is equivalent to "very."

Both are correct and extend the same meaning.

Both sentences are correct. 😊