AO Smith and Rheem are both high-quality manufacturers. I don't consider myself biased, I am actually a Bradford White fan, but I hear their quality has dropped in the last few years, maybe not. BW is / was known for great gas water heaters.
I can tell you from working for Rheem as a consultant, they put a lot of research and development into their products. They make a LOT of water heaters and probably have more market share than many think.
With that said, I have a Rheem Performance Platinum LP Gas burner..... and for the second time in less than 8 years, I had the burner assembly taken apart while laying on my laundry room floor this weekend to clean the fouling off of the pilot assembly from the oil in the propane. It's not Rheem's fault, it the fact that my tank is nearly 30 years old, we've let it get down to less than 1% twice in the last 7-1/2 years....
I'll say that trying to find a new burner / pilot assembly without a serial number has been a complete PITA. Why don't I have a serial number? Well, I bought this at a scratch-n-dent store that sells a lot of HD stuff and paid about 1/2 price back then. Today, that price is about 1/3 of the cost of a new water heater.
If your daughter has the water heater in a location that will benefit from air conditioning most of the year, a heat pump water heater will cut her energy use on the water heating by 50% or more. You just have to know that in heat pump mode, they put out a lot of air conditioning to the space they are in.