Well Julie, the Achilles' heel of a Cruze is the cooling system. First thing, nice job on keeping the coolant level up. This is absolutely critical you keep doing that.
My question to you is, have you actually seen the source of the leak? Because the way you described it, I have my doubts. For now, lets awesome it is the coolant reservoir leaking. This is a common failure, and with your mileage 100% expected. Get a Dorman replacement, they are better than OEM and 1/3 the price.
Here is the deal it is a $20 part, that is very easy to replace using only basic tools. I actually replaced mine a couple weeks ago, it only takes a few minutes. if you bring it to any shop your looking at a $200 bill.
That said, judging by the amount of coolant you are losing the reservoir isn't the source of the leak. It is your water pump, if the water is coming from (and leaking down) the passenger side of the engine compartment. Bob is your uncle.
but not seeing one where it’s leaking with no indication of overheating?
This is very common issue not many people understand. The engine coolant normal operating temperature is about 230F. If you have a leak, but you still have coolant (and this is a huge butt

), the car can't "overheat" because water at atmospheric pressure can't get hotter than about 212F.
One of the most common failure modes of the water pump is the seal goes bad. And while the car is running probably won't leak that much, but about an hour after shutting it down (or maybe less) the seal cools releasing the coolant from the engine. Regardless of the leak location, I still highly recommend replacing the coolant reservoir.