I too have not had any problems growing clematis in pots and leaving them outside. Once again, growing zones do not give enough info to use that as the ultimate decider of whether clematis will survive outside in pots since the zones only give you average highs and lows. What would be more important is the overall size of the container you are growing them in, the exposure the pot is in (direct sun or sitting in partial to full shade all day during the coldest days) and how long on average the plants would be exposed to frozen conditions in your pots.

Are you planning on keeping it in a container. If so it needs to be a large container. I grow a couple in half wine barrels but would not want to keep one in a smaller container for long. If you are going to put it in the ground I would do so as soon as possible. Plant it and fertilize it with rose fertilizer and it should bloom for you this year. It sounds like one that blooms on new growth (type 3) which should be pruned back each year. Provide something for it to climb on.

Crystal ~ I thought to post this *OverWintering* album to show as well as ask in this Clems Forum, if my efforts w/ Hydrangeas (in my zone) would be sufficient for Clems in containers left outdoors. These pics demonstrates part of the step by step I do to protect old canes. Since Clems are pruned down it would not be as meticulous as protecting Hydras. My front faces NW & get blizzard/damaging winds wrapping around the back so I decided to wrap landscaping (black) fabric around the cages to help cut damages. Snow is a great insulator but we don't always get enough. The Nikko w/ a rose-cone-hat is a tall shrub & I needed to cover the bundled top. The black portion you see at the bottom in just the same landscape fab wrapped around the cage. As mnwsgal posted, she uses the dry leaves-filled bags & is sufficient in her z 4. It works very well for me as well. I've also used thick cardboard boxes filled w/ leaves turned upside-down held down w/ bricks on top (rose cone style). In your z 3 added bubble-wrap around the container might help. Let's wait for others' comments. I'm adding a few more Clems & Roses in Spring but have to keep them in containers over this Winter & am trying to learn as well, how to protect them. Thanks for viewing the album!

How much sun does the balcony get? Clematis do require a minimum of 5 or so hours of sun a day for proper photosynthesis although they might get by with less if they have bright indirect sun. I would buy as large a pot as possible to help prevent the soil mass from freezing solid over the winter. I would also tend to stick with a type III clematis since the top growth is likely to get frozen back to the soil line each year and depending on your mom's microclimate, may not emerge until later in the growing season. If she goes with a type II, then she might not get blooms due to the length of her growing season. Does she have somewhere she could move the pot over the winter so it wouldn't be exposed to the full brunt of the cold winds over the winter? Perhaps she has a storage closet on the balcony that the pot could be moved into over the winter? The bottom line is that if she really wants to try growing a clematis on her balcony, why not give it a shot with a type III clematis, perhaps even a couple of integrifolias, in a large pot and see how they do? Trying to guess the microclimate for a specific location like that is going to be difficult and we have all found that experience and trial and error are the best ways to find out what we can get away with and what we can't.