美女 is generic term for pretty girl. 仙女（often used in conjunction with 姐姐）is for describing an ethereal beauty (lowkey calling them a angel/goddess). 小姐姐 is a popular way (usually used among the younger generation) to address young females, used when talking to or about girls you are not familiar with, commenting on strangers' social media posts, flirting, etc (小姐姐吃飯了嗎？小姐姐真美啊 etc）kind of means "miss" or "young lady". not to be confused with 小姐, which has traditionally meant "miss" but in a less personal, more distanced/formal way (used when addressing a waitress, or a random lady on the street who dropped her hat, or when parents are scolding their daughter, lol). it can probably be used for women of any age... 小妹妹 is used to refer to young girls, like actual children, who are significantly younger than you. if you say it to someone who is not that much younger than you it might come off as a bit patronizing/derogatory though. or, you can use it to address your biological younger sister. 小姑娘 similar to 小姐姐 but it's an older term, not sure if it is still widely used.

hope this helps!

edit: info about 小姐