Sims with insomnia?

That's related to bars or similar. Don't stick around until the bar closes, but leave beforehand, or your sim wakes up every night at the time the bar closes and sims get pushed out of the door. Just reset the sim.

Hey, @Turjan and @KevinL5275 thanks for the replies!

I haven't discovered what was making my sim wake up. I usually save at 3 or 4 in the morning (while they're sleeping); quit the game and come back. I also have them use the phone so that the game can be paused at the moment they wake up so that I can manage their routine.

I decided to go with the flow and changed her heavy sleeper to light sleeper and, so far, the behavior stopped.

Any negative moodlets when she wakes up? That's unusual being a heavy sleeper. Any other radios or TV's on in the room or in the house?

You could also try resetting her.