Dude, pm me a pic so long.
The last 3 women I've met have been bat**** insane and had been trying to get me to take a level of interest in them that they thought was reasonable.
It's not good to lie, as that will just come back to haunt you in another way. You can't be scared of her, which is why I need a pm so I can tell how big or angry she looks

you can be firm with her without trying to intentionally hurt her, even if she takes it that way.
You say she has a boyfriend, raise that with her and say that you wouldn't appreciate your girlfriend spending that much time with another guy, if you believe that.
Start petty arguments with her like your stance on abortion, religion, homosexuals, politics, etc. Right now you might be appealing to her because you're mysterious and you haven't bent to her will yet. This isn't going to happen quickly, but it is the safest way to go if you have to continue working with her, you need to help her lose interest in you without rejecting her, or else you're going to unleash a whole other demon