Ahhhh, call me jealous.
You can probably find some of that terrain at all of those places. Personally, I found Schlick to have a harder average of terrain -- not the hardest runs, but I felt the average run was harder (if that makes sense). Of the three, Axamer was my favorite. When snow is scarce, I found that Stubai has the best snow (as it is "the glacier", and thereby the highest elevation.) She would probably find the most to do at Axamer (but it has been 2 years since I last went). BUT, the ski bus goes everywhere (and is free). Feel free to check it all out. And as a snowboarder, she should be better able to handle it than a begining skier. Snowboarders are far fewer than here. I think Stubai is the farthest out of town.
Of course, you'll have a great time. The Austrian people are wonderful and gracious. Avoid the weekends as they can be a zoo (to quote a local -- that's when all the Germans come to ski). It is a different experience from the states. They start later, and are in no hurry to groom the snow and open the resort (unlike Mammoth, where the groomers start as soom as it is safe).
And . . . stop at Kaiser Stube and tell Alex, Klaus and Joe that Casey (from Father Tim's group) sent you. Awesome food, great prices and they have menu printed in English.
Let me know how you like it.