A few ideas:

Put her hand in a bowl of warm water.

Use something loud, like symbols or a trumpet, to scare the shit out of her.

Get a fake cockroach or something, and put it on/near her. For a fake spider, you can use fishing line and dangle it above her.

You could also try subliminal messages on her too. You could start working on certain traits, and conducting experiments. Slightly unethical because she didn’t give you informed consent, but she gave that up when she decided to violate your privacy.

Take a bucket of cold water, and slosh it over her.

Get some eerie lighting/a scary mask (grotesque possibly), a prop axe, a bloodstained nightgown, and a red floodlight. Change out of your regular clothes, and then the the light on. For added effect, if you can, get a buzzsaw/chainsaw.

Take a fully inflated balloon, and pop it near her ear.

Tell her to sleep on the couch, or lock your door.

Based on the type of person your mother is, you may/may not want to do some of these. Wishing you all the best!