If she has never done a hammock before, I can envision your poor mom having all kinds of problems getting into or out of a hammock and staying in there without falling out. They can be tricky if you are not used to it. And if your Mom is not fit enough to go on a long hike, getting in to a hammock can be a challenge.
While it's bigger you can probably find a folding recliner type chair which might suit her a little better. That's what we used for my mother-in-law... her, her nice chair, a wrap around blanket, a good book and she loved it. She never fell out once! She wouldn't even go near a hammock.
You might try asking her, but don't talk her into anything. All the very experienced (okay, old) Mom's I know don't complain, just do the best they can, have a miserable time, and say they had a great time anyway. Mom's are the best but they are always too upbeat for their own good.
I hope you find something.