SOuthern,
They sell little toddler beds, that actually become regular twin beds for her when she grows.
Look around on the internet to see what I am talking about.
It might be worth it for you to buy one, so in the future, you can use it for her again. or anyone, once it is a twin bed.
I would also buy a rubber sheet where you expect her to sleep on the bed. Saves the mattress.
Have her parents bring the teddy bears and toys she sleeps with now, or if she doesn't, go buy her one and send it to her a week ahead of time, and have them bring her with this teddy bear.
I would put her in her own room, even if its a strange house, just leave a small light on all night for her. That way when she wakes up during the night, she won't be afraid.
How nice your getting time with your granddaughter, I hope you enjoy the visit.

We invested in a few blow up mattresses for when our young grandkids visit. A 2 year old doesn't weigh much so you don't need to buy the very best. We bought a mattress pad and some Disney themed sheets. The kids make a beeline to "their" beds when they get here. They set up their stuffed animals and handheld devices on them.

Pluses are - if they forget where they are and roll out if bed, they don't have far to go. The plan was for them to sleep in their own room down the hall from Mom, but I think they got separation anxiety in a house they don't stay in too often. So the beauty of the blowups......they just dragged them to the foot of Mom's bed and everyone felt cozy.

Low cost solution too. As they get older, we'll have to figure out something else. But good for now.