I too am very security conscious but only an out and out loony would tell a guy she was going to get a knife. If the guy turned violent after she said that she wouldn't have time to go and get it.
being security conscious is not an excuse to accuse someone of raping you, when you had been paid to have sex and no sex had even taken place. someone asking for more lube is also not an excuse for making threats of violence or actually hitting someone.
Even if she really wanted him to leave all she had to do was give back the £100 as he had only been there under 20 minutes so £50 for her for doing a half arsed job for 15 minutes (he had a shower) is a fair price. All she had to do was politely explain she didn't feel comfortable anymore so here is what you asked for back so now please get dressed and leave.
I have had to do this before but gave him a full refund just to get the situation dealt with as quickly and as safely as possible. I am sorry but being safety conscious makes you want to get away from the situation as safely as possible as does not include hitting someone or threatening to take a knife to them. If she did this to the wrong person she could have been seriously hurt.
This has nothing to do with security fears and is more to do with being unstable. In any situation of conflict the best we hope for is a non violent resolution. Its part of our job to be able to do that. To stop it escalating. This nutjob escalated the situation to a point that she had no control at all. Anyone less in control of themselves than the OP may well have decided to fight violence with violence.
She needs to quit this job as it is not for her. De esculation is one of the very first tricks we need to learn and she has only learned how to escalate a situation.
This is one who needs to go straight into the Hall of Shame as soon as it is sorted not just for punters sakes but for her own safety as she is asking to get hurt