Why do I have to....

So I just started my new job about a month ago and I was told to have to go to a different office tomorrow. I did voice that I don't feel as if I'm ready to go to another office where I will be by myself all day. The reason I have to go over my coworker who has been here longer is because she just doesn't want to travel to another office. I'm already feeling anxious and nervous. I know I have to just put on my big girl pants and just do it.....but I don't wanna 😳😩🤦‍♀️