in zamiast at? She's got a good opinion about the hotel we stayed at.

In my view 'at' in this sentence sounds more naturally.
I checked the Internet too and it looks like in most cases in/at can be used interchangeably when it comes to hotels though some ppl specify that 'in'would mean the building itself and 'at' could mean that somebody is on the grounds of the hotel. But honestly I don't think it really matters which one you use :)