señorita is usually used for single and or teen girls in Mexico.
You could also use señorita referring to a little girl like: "esta señorita" or "mira que señorita" when a little girl dresses like a lady all fancy and stuff, or just to boost her confidence
it could also mean pretty depending on your tone of voice and how you use it. like if your at a club and you say "Hola señorita" to a stranger it makes a girl feel young and pretty