The BO thought she found a great way to make a profit by stall sharing.
She found out the hard way that her profit evaporated by the expectation of boarders that their horse would have a clean stall and clean and full water buckets.
Having to clean stalls and water buckets more than once a day will blow through any extra money very quickly especially with the price of shavings these days.
Rather than admit to her mistake she opted for cutting corners.
I imagine you are not the only boarder who has voiced her displeasure even if the BO has not disclosed this fact to you.
Stall sharing makes sense from a BO s stand point but not for a boarder,imo .
Is the BO going to foot the vet bill if your horse or any other contracts a communicable disease?
I understand that liability could be very difficult to prove in a boarding situation but in the case of your horse who seems to be very sensitive, it seems to me that if she were to get some kind of skin disease it could be directly linked to the condition of the stall.
I get that you like the training your horse is getting, but I would try to find another place to keep your horse.
This BO is cutting corners and doing some dangerous things in my opinion. And she wont be paying any of the vet bills either.
Yes, horses do get hurt, but she doesnt seem to be making any effort to mitigate the risk.
Ultimately it is your decision, but I think you should look elsewhere. And I believe you can find another trainer who will suit you just as well.
Good luck