My new RES turtle is extremely shy, Why?

I have an adult RES named Elliot, an Eastern Painted named Farley, a Yellow bellied named Rocko, and just recently got two baby RES, who all get along well in their 40 gallon, I just today got a female RES, a little bigger than elliot, (Fist size) and the other turtles eat out of my hands and minnows/goldfish ect, the newest RES is very scared and I will rarely catch her basking, if I do she dips as fast as possible, she eats just not when I'm standing over or near her, when will this stop?