The employee who took me to my new job is the same as I was in 1995, equivalent to my boss, surnamed Liu, because he was called Xiao Liu because he was young?

She was born in 1995. Like you, she is also your boss. It is definitely not appropriate to call her Xiao Liu, nor is it appropriate to call her Sister Liu. You can call her last words and sister, even if she is a few months older than you. Girls generally don't care about this, but people who call her sister and aunt care most.