Near the end of our second break she started to talk about her financial situation and getting X-mas presents for her children. I had my head buried in my phone playing a game and ignored her. After a minute or so she switched back to work talk, then left. I looked up at that point and realized that we were the only ones in the break room. Looking back I now realize that I should have paid a little more attention to when everyone left the room, so I could have left with them.
I'm really and truly struggling to see how you accidentally ended up in an empty room with her. Playing games on your phone? You're not a teenager, Scorpio.
You don't owe us anything, but you owe yourself and your BSO some honesty. If I had to guess, I'd say she got you alone for some conversation and you blew the boundaries by giving her what she wanted (attention, personal conversation) because your conflict avoidance kicked in full steam. You don't offer a cactus a hug. Your walls weren't up. Inside you were likely VERY uncomfortable, but you haven't learned how to say no yet.
If what you're reporting here is close to accurate, she's definitely a predator and she knows how to manipulate people like you.
Take a deep breath, and arm yourself with love for your BSO, respect for yourself, and the law. You have to take an active role in getting her to stop. This is going to escalate, so doing something about it now isn't going to make things worse, it's going to give you more control.