No you can't say it to a girl because it's a male term. You could use 'you are a sweet girl' or just 'you are sweet'. Hope this helps :)

Only girls call each other "guys". So it is alright if you are a girl. If you are a boy, DO NOT say "guy" to a girl. Unless you are gay, of course.

“guy"用来形容男子，不可以单用在女孩子身上哦，呵呵` 不过如果有一群男生和女生在一起的话，那么你可以问：Hey guys!意思就是大家好啊！这时候guy就既可以形容男生也可以形容女生了。