Mom is always around, how do I do things (get hidden cookies, turn gas valve on stove, etc.) that I don't want her to see?

How is ig going Kimberlitas?

Yes, its weird. They can't remember something 5 min later but like a child, the watch and learn.

Learn diversion and distraction techniques.

If you cannot find how this is done, study the behaviors of a family member with narcissism or sociopathic personality disorder. They have been doing it to you for years. Once you become aware, then you can try to use it to distract your Mom, or divert her attention away.

It may take some practice, but I think it can be learned. Your goal is to use the technique for good. That is different how the narcissist or sociopath uses it.

Are you in her home? your home? Are these things that you must do everyday or is it "once and done"? My dad is in assisted living and has a full apartment, including a stove and oven that I didn't want him using. While he was out I just removed all the knobs. Had he watched me doing it we would have had a fight on our hands. Can you do these things when there is a friend around to distract your mom? or while she's asleep? If it's things like making a cup of tea and you don't want her to see you turn on the stove try suggesting that you have tea in the living room or on the porch and that you'll bring it to her. Then don't start the kettle until you have her situated in the other location. I think deflect and distract are your only options if you can't do it when she's not around. I can imagine that thinking through every step of every activity to assure that you aren't "teaching" her something potentially dangerous is very exhausting.

Become sneaky.
Get the cookies out, cover them in a pan or something, go to several different cupboards, drop off the cookies in the fridge for a second, distract her by sitting her down for tea, then bring the cookies to her, if she is watching, take the cookies back to the fridge. By the time she's looking for them, they are no longer there in the fridge, right?

Keep the gas valve for the stove in your pocket. You know, the one you just retrieved from the magical fridge that stores e v e r y t h i n g......then use it to cook, return it to the magical fridge if she is watching, then when she goes to find it, it is not there.

Practice sleight of hand. There must be videos online to teach you this.

There is also a limit to how many maneuvers in a row a patient with dementia can recall.