Best way to stay hydrated(elderly mom is sick)

[SomeJackleg]

Hi all.

So my mom is 85 , and has been sick (possible stomach bug or food poisoning) , since sunday morning.
I think food poisoning as she said that she had eating some salmon that tasted bad. 

She has not eaten, thrown up a few times (maybe 2 or 3 times), and maybe drinks 2 , maximum 3 glasses of water a day.

She's very skinny and frail as it is, so I'm worried she may be getting dehydrated and lose too much weight.
She seems to go up and down a bit. 
Sunday was bad, yesterday better, and today a bit worse then yesterday again, but a while ago she seemed a bit better again.
She has no fever, though for a little while she had mild feverl.

I'm thinking about getting her some nutrional drink ?  She's pre-diabetic and has to watch sugar, but now off course she hasn't had anything to eat a few days. Would orange juice be safe to give?
Any suggestions?

Thanks

Brawndo the thirst mutilator, it's got electrolytes.  sorry i couldn't resist  .

but as it has already been said, Gatorade or Pedialyte will be about your best bet.
you might even try one of the flavored water powders, two i really like are Strawberry Crush or Welsh's Strawberry Peach
zero calories.

i personally chug water all day long.