Guia and correcta
First, why does "Guía" have a accent? I don't know how the accent rules apply when there's a tripthong and no second to last syllable.
Second, do you say "Correcta or correcto if you are telling someone that she is right as in she answer the question correctly.
I think it would be correcta because respuesta and chica are feminine. But correcto too because whatever it is that she said could be shortened to "lo".
2 Answers
Guía has a tilde to show that there is a hiatus, that is to say, í and a are not in the same syllable. GUÍ - A.
You would say correcto (if you are just saying that word) you could also say: la respuesta es correcta.
See my answer to the thread "How do we know when and where to put accents?" It is now in the Q&A.