My Mom Is Trying To Take Legal Proceedings Because I F(19) Want To Move Out.

Location: Washington

I f(19) am currently a student and have been living with my mom and her boyfriend, but recently her boyfriend has received a job offer in Florida. My mom told me that she doesn't want me to move with them, and to figure out my own living situation. They mentioned that they plan on moving within January or February, so this gives me some time to figure things out. I'm working at a warehouse that pays $22 an hour, im working 20 hours a week right now but just scheduled myself for 40 hours a week starting December 1st. I applied to my schools housing program, but my mom found out about this and is now threatening me with legal proceedings. It appears to me that now that I'm on a path to actually leaving home, she no longer wants me to stay behind while her and the rest of my family move to Florida. She is threatening me with legal proceedings, and says that even though I am 19 she wont let me stay behind, and that she believes I am a danger to myself. She claims to have spoken to an attorney already who said that I have to move with them (which I don't believe). She says that she is going to say I am not in the correct mindset and will harm myself or others in order to make me stay with her. Is this a valid way for her to make me stay? Is it possible for her to keep me at home even though I am 19, well over the age of 18? Im absolutely baffled by her behavior. I'm a student with good grades, currently working, don't do drugs, smoke, or drink, I do all the chores at home, and if allowed I only go out once a week with friends and usually come home before 7. I have no criminal history, or history or harming anyone else. I have a rough past of depression, but have been doing counseling for years now. She has withheld my funds from me (roughly $4,900) as "safekeeping", she has permitted me from learning to drive or get a car, and when I first started working she tried to control the amount of hours I would work and even called my previous employer on the daily. I really just need advice on how to go about this, I'm tired of all the stress she has placed on me these past few years, and really would appreciate any help.