Depending how mobile she is you may need a camera in each room. Also depending on what you are looking for are you prepared to put a camera in the bathrooms?
Does she live with you? If she is still in her own home and requires 24/7 and you are concerned about cameras and safety I would probably just look into a nursing home. What happens if a worker calls off for a shift?
I worked as a nanny/babysitter for a family that had their WHOLE house wired. I suspected there were cameras, but did not find "proof" for 6 months. It never bothered me. They paid well, were reasonable people, and the kids were well behaved for their ages. I am sure there was film of me naked--changing to go swimming or after a particularly messy art profect. Once I found the cameras I did confirm that the powder room did not have a camera. When I left the job (Dad's business went belly up and he was staying home for the summer) I made a comment hoping there was no "tapes". The Dad confirmed the system recorded constantly for 72 or 96 hours and then recorded over the same information.
They also had some sort of motion detectors that sent an alert if someone entered different rooms. At that point he complimented me on not going in parts of the house that I had no business. For example I worked there for 2 years and only walked into the parents bedroom one time--when one of the kids went in there and would not leave. The door was always open, but I had no business in that area of the house and encouraged the kids to stay in the "kid areas". Basically I tried to keep the parents room, dining room, office, and guest room kid free. I think just the basement, parents room, and office were "wired". I only went in the basement (unfinished) one time when we had tornado type weather.
There are many technology solutions you can use, but ultimately you have to trust the people watching grandma. When my husband's grandmother lived with us ( a 95-99 year old with dimentia) we had a camera on the front door that was activated when it was opened. We were more afraid of Grandma getting out and having no information. It was never used, but it is still nice to have to decide if we want to open the front door. No unwanted solicitors. My husband hooked up the video feed to a TV channel so we can see the front stoop. Our "system" was a cheap
Sams club kit.