Is the nutritional drink Boost considered a good way to add fluids to the body when the senior won't drink much water?

Pedialite Is also good. They have Popsicle.

Yes, any liquid is good.

Any of these might also work
Popsicle
jello/gelatin
juice, I would dilute it a bit but you still have the flavor
fruits
Any fluid is better than none.

I'm sure it is better than nothing. Would she drink Gatorade? I personally don't like drinking water, I prefer sparkling mineral water with a tiny bit of cranapple juice in it or diluted Gatorade. Maybe give that a try.