Was it a bag of Maltesers ?
Yes, it's outright theft. A PP said she'll be after your money next.
She will deny all knowledge of swiping the chocolate and you will end up looking petty and/or paranoid. Hope this isn't the start of some genuine gas lighting.
I suspect her making the telephone call (on her phone or your phone if you have one in the kitchen ?) Was an excuse to be in the kitchen. Was it an important call or was she just bored ?
How come the cheeky bitch was rummaging in your fridge anyway ? (Not because she was peckish, it wasn't something Like cheese, was it. Oh no, it was a treat she helped herself to. The whole chocolate bar. Grabby and entitled. She would have gobbled it really quickly too. What finished first I wonder, the chocolate bar or the phone call ?) Sorry, but this is how it starts. If she comes round again, I wonder what she will be up to.
What will mysteriously disappear next time she comes round ? Just little bits. Have you got a jewellery box ? Do you leave your purse/handbag out of your sight ? Do you have nice ornaments or c.ds./d.v.ds.
She sees you as a push over and your property as nothing more than fair game. Sorry.