Be sure to clear the area before summoning Shy, as her and Sian might fear you into any nearby mobs. Also make sure your mana is full, and have some mana pots with you, that way you shouldn't get too low.

It helps if there's someone with you who can freeze, in case Sian breaks your trap before taming is finished. I had a mage help me with that, after I helped him with Shy.

And no, the mage's frost nova will not break the taming. I assume another hunter's frost trap wouldn't either.

I pulled off this very difficult tame 2 days ago, with the help of a 57 mage, on the Whisperwind server.