I don’t think trying to clear the mind works easily for people like your wife. She could try thinking about something pleasant and rather mindless, but maybe her thoughts will still intrude on it?
It’s a skill to be able to compartmentalize. I am better at it as I get older. I only allow myself to obsess or ruminate for a while and then can switch it off usually. Unless, it’s something very traumatic.
Typical recommendation I give are don’t drink caffeine late at night and don’t try to go to asleep until you are ready to fall asleep. Try reading, try watching TV. Pillow talk with you at night. Something that replaces her thoughts.
I’m not so fond of go to sleep drugs, but it’s worth mentioning that several years ago Ambien became the first drug ever to have a different initial recommended dose for women than men. For years it was the same, but women were having a lot more side effects. In fact, the side effects were observed during the trials by gender, but the scientists chose to ignore them assuming doctors would always first try a low dose, which I would hope they would, but they don’t. Your doctor might have no idea, or just prescribe what he has prescribed the last 20 years.
I think the initial dose for women is 5mg and men 10mg, but you could check with your pharmacist. If she was started on a higher dose she could try the lower. I have no idea if you can split a pill, again a question for a medical professional if you choose to try.