My friend ALWAYS wants to hang out!!?

She has no life and shes a person who always sits on her @ss and doesn't do anything with her life. She doest have hobbies or sports so she always wants to hang out with me. Shes mean so nobody really likes her. Im the only person who always gives her a second chance. And shes depressed and taking prozac right now. I tell her she cant come over but shes always reasoning out with me. I keep lying to her but she always finds a way and a reason to come over. One time she wanted to sleep over but my dad said no so she said this to my dad "Why cant I sleep over? Do you hate me? We wont be messy I promise" My dad said that shes too forward and she has no shame. Everytime she wants to hang out even when I dont want to Im always giving in to her. How can I not be walked all over but tell her nicely?