Mother doesn't want daughter to grow up?

After a few months of not visiting home (background: I am an 18 yo college student with a summer internship at the university), I'm finally coming back. My parents like to visit me every month, however, so it isn't like I haven't seen them in a long while. I intend on spending three weeks of my summer back home, and hopefully will return to my college town for the last two weeks of summer to spend time with my boyfriend. My mother would much rather I stay all five weeks, even if it means my being stuck at home with no car to go anywhere, friends having already left for college, and parents away for most of the day at work. She's being irrational about making me stay, but that's partly due to her unchangeable overbearing, controlling nature. I want to vocalize my desire to go back to my college town early, but doing so would entail a nasty fight and her getting unnecessarily furious with me and my boyfriend, to the point she would either cut me completely out of her life, withdraw her financial support for my education, or force me to attend a college closer to home. My family is very close, and I could not imagine not having a relationship with my mother, but it seems like the only relationship she wants with me is one in which she still has control over me. How do I resolve this issue with a mother who refuses to let her daughter grow up and pursue her own life as she transitions into adulthood?