The brands you looked at are likely best choices for her intended use, but I've no experience with them. My FW is a 4 season, but in reality, I'd not want to use it much below 20 degrees, for an extended time. Mine is well insulated, with good plumbing protection. IMO, no matter the model, keeping warm is not as big an issue, as moisture control. An experienced Winter camper, willing to go to the trouble, can likely do this. I think it may work for her along the coast, but trying to tow it to, use it at the higher elevation, colder temp ski areas may not be best choice for her.
Jerry