You might be surprised. On an indoor board with corridors -- or alternately, Ice Pillars in front of Rasputina to block enemy LoS and then use a flanking model to bounce spells off of. Basically, anytime Rasputina wants to hide from dudes and still shoot them. I would suggest giving her a try without worrying about how you're going to "set up" Ice Mirror and just take things as they come, it might be easier than you think.
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Rasputina was my first demo game and the Ice Pillars were actually a big sell for me. My Warmachine/Hordes army has a character who is supposed to magically sculpt stone to her will, and the rock wall she makes is about tall enough for Charlie Brown and Linus to rest their elbows on -- but not for too long, because it goes away after a round. Getting to make ice columns that were 20 feet tall (in scale), and weren't going anywhere unless you dealt with them, felt like a real magic spell by comparison.