Sleep Walking.

Home depot has those inexpensive motion detectors for doors that beep if the door is opened. You can also place one in the doorway of her room, as leaving the house is not the only danger - she could turn on the stove or countless other things. Also, a baby gate in her bedroom doorway - she may not be able to get over it.

You can also try the child proof knob covers, she may not be able to maneuver that while sleeping.

Since you are up with worry, you can monitor how those things work, or need to be tweaked.

Blessings!

We have an alarm and leave it on chime so that if the door is opened it beeps three times. My kids have learned to sleep through this but I always hear it if my husband comes home when I am asleep. The other doors we have a flip lock on the top of the doors (garage and back door) that my kids can't reach. I think you can buy a sensor that will chime without getting an entire alarm system installed, but I'm not positive on this. Anyways, it may be able to give you some piece of mind. Good luck. It is scary having a sleepwalker. I had a friend growing up that ended up on the roof (they had a two story house) and they ended up putting bars on her bedroom window!

My oldest son and I are also sleepwalkers and with a husband who works nights, I totally feel you!!! We have a double-sided key for the front door, (I don't know if that's what it's really called), but you can lock it from the inside with a key and from the outside with a key. (It looks the same from the inside and the outside.) We lock it and take the key out, putting it in a secure place when we worry about our wandering child! We've had it for years and never have worried about losing it and locking ourselves in (we could always use the backdoor if necessary, or the garage if it came to it, though the most popular form of entry/exit for all of us is the front door, which is why it's what we've focused on). You can buy it at any hardware store and install it easily. Good luck!

Maybe it's just temporary, my kids have done it a handful of times, but maybe you should install some kind of additional lock that your husband can unlock so you can get some sleep.