MIL has me so frustrated! Any ideas?

You need to understand and read more about dementia. Your MIL's brain is broken. She doesn't have logic anymore. My mom had dementia as well. She'd tell me whatever I wanted to hear, like a little kid. Yes, she was taking her medications every day (she wasn't). Yes, she ate the leftovers in the fridge (she didn't). She wasn't maliciously lying to me, she had lost the capability of knowing truth from fiction. In her mind, she was telling me the truth. She also lost any initiative she ever had. She'd tell me she was going to write her friend right after lunch. She never did. If you watch Teepa Snow videos about dementia on Youtube, you'll see her talk about the common behaviors that come along with the disease. Losing initiative is one common feature.

Paranoia is also a common feature of many with dementia. They think you're stealing from them or you're having an affair with the neighbor who is living under your bed. Their delusions and ideas appear ridiculous to the rest of us but are very real to them.

It sounds like maybe MIL needs more foods with a lot of water in them like fruits. Will she drink Ensure or other liquids like tea? Suck on popsicles? My mom also didn't drink enough fluids. She loved soda pop though, she looked on it as a treat, because she was poor growing up. So she drank a lot of pop that I brought her. At that point, any calorie and any fluid were good in my book.

Or try an "additive" to her water to make it look "pretty". I must admit, I haven't done this yet, but I have thought about doing it.

I was told by a nurse no pop or coffee, but my mil tends to help herself...at night...when everyone is in bed.

some older people don't want to drink water cause that means they have to use the toilet and its too much trouble. not saying that's a good thing.

maybe try one of those plastic (something safe w/o BVA? pvc?) drinking cups with a screw-on lid and a straw that comes with it. maybe she wouldn't mind sipping on a straw instead of from a commercial 'water bottle'

i know its hard when dementia involved.

ive even left notes in my moms AL room.
near the sink: "DRINK LOTS OF WATER"

my mom hasn't removed the note yet (she usually removes my notes) and i have no idea how much she consumes everyday.

Thank you everyone for your responses. Blannie I've worked in senior housing for 20 years and my fil is in a nursing home with Alzheimers so I actually do understand quite a bit about dimentia. Its just that its harder to cope with and see as clear though when it hits home. Your emotions are involved. I'm going to look for the videos you recommend and you make a good point about losing initiative. That is exactly what has gradually happened with her.
Lostinthemix I love your idea about adding a pretty color additive. We hadn't thought of that. Wally003 thank you for the tip about plastic cups with straws. That may work too.