Depending on the size and state of the clematis, I might be tempted to pot them up into one gallon pots and grow them out. You could then plant them in MA in late August to get them acclimated before your winter season starts. If they were potted up when she bought them and are of decent size, you might be able to plant them this spring. I would wait until after your last typical frost date to plant them. You might want to acclimate them to outdoor conditions if they have been stored inside in a protected area.

I would wait until the weather in your area begins to stay in the 60's. Plant them 3 to 5" deeper than they sit in their pots now. Through in a handful of bonemeal in the bottom of the hole & work it into the soil. After you are done planting keep the clematis watered & feed once a month with some Rose food. Keep them watered all summer when you don't get rain. Clematis like a moist soil & feed once a month or after a flower flush. If the plants are nothing more than some roots right now you will need to pot them up for this early part of the season & plant them in the ground in early fall when they should have a good root system by then. Clematis are not at their best until their 3rd season. That is when you will get the best flowering.

Thanks for the very useful information. I'll pass it along to my wife