Noisette is Bad at Making Treasure Hunts
I'm really not sure if Noisette actually wanted anyone to find her treasure, or if she still harbored a ton of resentment and fear towards the city and wanted to clear her conscious before death by making it appear that she had done the work to ensure it would be found without actually making it possible for someone to do so. If she really wanted the stained glass to be returned, she could have just written in her will "the stained glass is in xyz, please give it back the following places:"
Instead, if her goal really was to have someone find the hidden stained glass after she died (as she states in the game in her final letter) she was bad at following through on her goals. The fact that Nancy was able to do so is due to so many contrived coincidences that would completely make it impossible for her treasure to be found in the real world. To find her treasure you need:
a) access to her moulin. This is in IMO her stupidest move in the whole game, she was director of public works (or something like that) and instead of trusting the moulin to the city when she died she did nothing and let it go to auction to a private buyer. Literally the only person in the entire game who gives a shit about her and the treasure (Lynn Manrique) can't do anything to find it bc Noisette didn't ensure that the treasure would be accessible to the public
okay, so maybe she intended for whoever purchased the moulin to find her treasure. Nope! because...
(Okay, I have a lot of thoughts here and this ended up being really long so the rest is under the cut!)