I don't see a real big advantage to either model to suit this arrangement. All of them have a permanent bed for two, and the dinette would have to be set up for the third to sleep on. Any of these models could be adapted for your intended use.
If your mom is sleeping on the dinette, maybe a special arrangement with making it into a single bed, with the left over room as a standing/dressing area, could be done. A curtain could then be drawn across that opening.
If you are wanting a privacy curtain drawn anywhere, whether around the bed or the dinette, knowing this ahead of the build would be a good thing, as Reace could likely put in some appropriate backing/blocks under the vinyl for support.
I am sure you will get lots more great ideas from the riff raff here.
It is great that you are giving your mom this opportunity, kudos to you.
I have brought my mom (78 ) on an extended weekend once, and will likely do it again. She has stayed in our trailer out at our rec land too. We have not bothered to do the privacy curtain, though if there was more of this type travel, I am sure something would be done. There is a bed in our cookhouse there, but she wants a toilet handy for night time trips, ans does not want to trudge across to the outhouse in the middle of the night.
Though, just this week we solved the issue of her staying at our land, in a way that will encourage her to come out more often, as she always says she does not want to be a bother. We just picked up a 1986 17' Bigfoot in really good condition as a 'cabin' to give her her own space. Though her first reaction was to grumble on us spending money, you can tell she really likes her new digs.
Even though she still drives fine, she is not keen on pulling a trailer anywhere.