1 选择that
（）she used to be为定语从句,修饰先行词girl.
从句中缺少表语,that可以在定语从句中作主语、宾语或表语.
2 还可以用who
3 不能选择what,因为根据语法规则,what不能用于定语从句.after ten years,she changed a lot and looked different from () she used to be那这道呢，请帮忙一下what因为这个空格引导的是宾语从句（作介词from的宾语）