Should we try and prevent my grandmother from letting the dogs out?

My grandmother is in the early stages of dementia. She lives at home and I'm typically here to keep an eye on her during the day until my parents get home from work. For the past year or two, one issue has consistently come up and it's driving a wedge between her and the rest of the family. It involves the family dogs. For the record, these are not her dogs but she enjoys their company and spends a lot of time with them during the day. But they do not sleep in her room at night.

The issue is that she lets them outside every two hours when they really don't need to go out more than a few times a day total. Sometimes she forgets and repeats the cycle (for example, she'll let out the first dog, the second dog, the third dog but then she'll start over again and let the first dog out again and so on.) She does this because she claims that the dogs 'tell her' they need to go out.

In reality, the dogs are manipulating her. She stands in the kitchen and gives each dog 5 or 6 dog treats EACH time she takes them out. We can go through a box of dog treats in days. What's worse is that sometimes she'll only take one dog out because the others won't go outside probably because they were just outside and realize they don't need to go out to get treats because she will still give every dog the same amount of treats if one goes out. If I'm keeping an eye on her in the kitchen and remind her that the other dogs don't need treats, she'll take them into her room, and the real problems start. She'll feed them chips, crackers, jello. She believes it is perfectly acceptable for the dogs to eat anything she is eating. Several of our dogs have gotten sick and thrown up and we've caught her giving them food that is poisonous to them like grapes and chocolate cookies. If I catch her doing this, it's hard for me to hide my exasperation. When she asks why she shouldn't do it, I tell her it's because it's not good for the dogs and we've asked her not to. This behavior is also compromising the training the dogs have received. They beg for human food, they run away when they get let outside and they manipulate my grandma for treats. Two of the dogs no longer eat their dog food because they are so accustomed to human food. One dog doesn't even like the dog treats anymore because she's given them so many so instead she gets human treats when we're not watching.

I tell her every day that she should just ask me and I'll take the dogs out, and she seems appreciative when I do take them out but then 20 minutes later I'll hear her taking them out again. I think she is taking them out as a form of entertainment or because she is bored. But it can also be dangerous. She's fallen outside before and not been able to get up and had to crawl to the door. I've suggested to my parents that we should get double locks on all the outside doors so she can't take them out anymore but I wonder if this would be considered cruel (if she's doing it because she's bored) or even a safety-hazard?

Any help or input is appreciated.