You are competent to make a great choice with Amber! She's a rare find in a semi-legit spa—she's young, has an amazing body, and gives fantastic massages. Most semi-legit spas have girls of all ages (to be fair, not all the other girls in SL are mama-san age, 40+s; many are in their 30s), and you might have better luck finding young girls in FS shops.
Another outstanding girl similar to Amber is Lulu. While not as young as Amber, she's still close in age and boasts a fantastic body. She also offers top-notch massages. DareDavil is a close friend of hers and can provide you with further information about Lulu.
Cici and Yui are young and good at services, but their massages are not as good as Amber's.