Print out a schedule of how you need the day to go. Present it to her and tell her that this schedule will be implemented at a certain date in the near future. You can offer her a brief explanation. Taking to long to explain something makes it sound to a female like you're trying to convince her of something so dont take too long explaining. look at her very seriously and tell her this is not a joke, you will be locking the doors or physically removing her because you need to focus on your work. If she comes in as usual, make it obvious it isnt the same as before by handing her the schedule and putting on earplugs, then do not acknowledge her unless it is to physically remove her from the garage. (Editing to add:) surprise her with a super soaker the first time she infringes and you will have set the tone in how you expect to be respected while you're working that would work IMO