You have allowed this woman to move her couch and TV and kitchen gadgets into your head where she has set up housekeeping. As long as you let her do that, then you will feel like shit.
You need to change your entire approach towards her. She sounds like a world class be-atch, but so what, there’s plenty of those types of people around, that you will encounter throughout your life.
This is what you have to do (unless you’d prefer living your life the same way, and having the same exact outcome). You are going to fake liking her. You are going to stop telling yourself that you hate her (even though you do, and that’s OK) but stop telling yourself, your boyfriend and us that you hate her and cannot bear to be near her, or else you will drive yourself into an early grave.
Accept that she’s going to be around you, either on purpose or by coincidence, then actively change your behavior. If you know she is coming by the salon, make sure that you are going to be there. When she arrives, instead of hiding in the bathroom, sit at your desk, and say to her, “Hi Bev, back for another party? Hope you and your co-workers have a good time.” What you want to do is kill her with kindness, because she won’t be expecting that pleasant reaction from you. If you treat her kindly (even though she doesn’t deserve it) whenever you encounter her, then YOU will look like a wonderful strong person, and in the meantime, you will become stronger.
Look forward to bumping into her and saying nice things (don’t ever say catty things to her, or you will be feeding her). She’ll either get bored of trying to get to you or she’ll actually begin to like you. Either way, she’s off your back. This may take a couple of attempts, but the payoff will be worth it.
If you see her in the street and she comes over, just say, “Hey Bev, how are you? I’m just heading to the store, how’s your mum?” Then continue on your way. Do not try to run and hide from her, or you will look pathetic.
If she texts your boyfriend, either politely ask (don’t demand) that he block her because it is very troubling to you. If he doesn’t want to do that, then consider that he may not respect you as much as you would hope he does, and that your relationship may not be what it should be. You may have to solve your relationship problem as a separate issue from the fact that his ex-girlfriend texts him (because she clearly still has feelings for him and is trying to upset you). But the ex girlfriend’s obsession, and your boyfriend’s lack of respect for you are 2 completely different problems that need to be solved.
Bottom line, kill her with kindness and become a stronger person.