What about using an old aquarium as like a terrarium? The sun would warm up the glass & make it like a miniature greenhouse, especially if she could use something tight-fitting on the top, like an additional piece of glass? She could get a 20gal or a 29gal (bigger would be better, of course), fill 1/2 of it with peat moss or something light like that it wouldn't be too painful to pick up, then put the pots nestled in the peat moss? Plus, keeping the humidity wouldn't be too bad then 'cuz she could just put some cool water in it once a week and let it basically steam on warmer or sunny days.
I've done this myself and I was able to keep a mini rose alive for a winter. But I kept this inside the house and not outside on the porch, so the temperatures were not freezing. I planted the rose the next spring outside and then we got a freak freeze that killed all new growth. Poor thing didn't stand a chance.
