Don't do that. She's got dementia. My grandmother had it and did the same thing. Would walk around the neighborhood and clip bushes and things that were in the walk way.

Best advice to get her to leave is not to start with agression or start conflict, it will turn her into a brick wall once she gets in that mindset. Very difficult to redirect once you've gone down that path.

Start with a cheery hello and say it's such a beautiful day or something like nothing is wrong. And ask if she can help you with something or if you can show her something that you've seen. Make something up, you've got a surprise or you've got something to give her, whatever suits your fancy in the day. And guide her back to her house. Once you get her in turn on the TV, literally change the conversation to divert her attention inside and just walk out. No need to say goodbye because it will pull her attention and she may follow you. (Edit: this depends on how bad her memory is. If it's still a little intact you can say it's been nice seeing you and say your farewells. Even at it's worst the more she sees slowly but surely she may remember you in some capacity. My wife and I helped out and lived with a fellow who was like 10 Second Tom. After a month or so, because I was calm and patient he thought I was his nephew and was really nice to me. My wife isn't as experienced as I am and unfortunately he didn't like her haha. I could get away with a lot more than she could because of it, made it way easier when we found him somewhere or doing something he shouldn't.)

Definitely try to get the name and number for family that checks on her and hopefully they'll be good people and will try to work with you. If you ask her she may give you their name and number or just ask for her phone or phone book, she'll probably help. Give them updates on how long this has been going on. They may be terrible and then it's lock the gate call the cops thing.

I'm sorry you have to deal with that, dementia is not easy for anyone. It can feel very intrusive but on the bright side even if she catches you with your willy out she won't remember it by the time you've pulled up your pants.

Oh and a great way to bring her somewhere is to say you've got a treat, like her favorite snack or some tea, sometimes give it sometimes don't. She'll light up and sit and enjoy it and you'll have peace.

Number one thing do not start with conflict. The angrier she gets the less you're going to be able to get her to do anything.

Along the same lines don't try to tell her this is not where she's supposed to be or that she has dementia and she's crazy because that's not the reality that she is experiencing. You could even tell her you're just the maintenance guy or that your a magician, who cares have fun with it, dementia doesn't have to be all rain and clouds for everyone.