I have a friend, her Chinese name is Dan Dan, her english name is Jillian, what is her full name?

Hi, Adlian. Generally speaking, people in China has a family name and a given name to form their full name. You only give me the given name of your friend, which is Dandan. So I couldn't provide her full name to you. You should ask her what her family name is. For example, if her family name is Li, then her full name is Li Dandan.