How to stop Mom from using the stove and appliances?

My mother has dementia and while she understands this and knows very well that her memory is extremely short, she still tries to be extremely independent. That's not a bad thing, but her obsessive behavior is a problem. She obsesses about coffee and wants it all the time. I found a brand of instant coffee that she actually likes that is decaf. Earlier in her dementia, she was able to make herself a cup of coffee, but those days are over. Unfortunately, she still believes she can do it and so she'll turn the stove on and then wander off and forget about it. Naturally she doesn't want it when I'm able to stop what I'm doing and fix it for her, she only wants it when I'm busy and can't stop. She insists she can do it herself. I'll tell her I'll fix it in a few minutes and she angrily stomps off. Two minutes later, she's forgotten the conversation and the whole thing starts all over again.

I thought about removing the knobs to the stove, but I caught her trying to make her coffee in the microwave. Somehow she melted a hot/cold plastic coffee cup in the microwave. Then I had to start unplugging the microwave and sadly she can remember to check that and she plugs it back in. The same thing with the toaster too. I thought the toaster would be fine, until she started messing with the knobs and so she burns her toast every single time!

I'm trying really hard to be patient but it seems impossible sometimes. I know she doesn't know any better, but I cannot come up with an answer. I have an open kitchen, so I can't hide it by putting up a curtain or a door.

I don't know what to do. She gets up in the middle of the night too and I have nightmares of the house burning down.

Any suggestions?