For a casita, any V6 SUV with available towing package (At least hitch and automatic transmission cooler) and a tow rating of 5000 pounds or more will be a comfortable and easy to drive combo. The casita ready to roll will weigh slightly above 4000lbs and have a tongue weight a bit over 400 lbs. assuming their longest model at 17' with most options. If she wanted a smaller trailer like the 13' patriot or another brand closer to 2000 lbs., most of the 4 cylinder cute utes with 350lb. tongue weight and 3500lb. towing capacity will make a great tow. I'm partial to Toyotas myself but there are a host of choices in this vehicle segment.
Now if you need any more info, we need to talk about how good of a cook Auntie is. ;)