|Hell must be freezing over because I agree with Hemingway.|
A restaurant that 'closes' at 9pm means they don't seat any new diners after 9pm. But someone who puts their order in at 8:45 (for example) gets their food around 9:15, eats until 10pm.
The servers and kitchen are cleaning up until 10:30-11ish. Depending on the type of restaurant, the servers and bus staff may have to do a lot of the surface cleaning (the janitorial staff does stuff like the floors and bathrooms) and they can't do the diningroom work while there are still customers eating. Like, a restaurant that does breakfast lunch and dinner service the night staff has to change over all table settings from dinner to breakfast setting. That's considered rude to rush the last diners by changing the tables around them. The cashier can't close the till until the last person pays.
Even at a fast food place there is quite a lot to do between serving the last customer and locking the door.
OP, not only does your post exhibit unreasonable trust issues, the reason for questioning her is because you want the relationship to be the way it used to be - that she's still available to go out late any night you want. People grow and change. Relationships adapt or end. Just because you're selfish wanting things to be the way they were, don't project it onto her being untrustworthy.
I think Penny had the right advice
You're going to end up being alone if you continue to act like a child.