That was a nice empty room she was in and the arcane lock could come down easily enough with a knock spell. But there were better ways to go about this. Instead what Zoltan does is he casts a simple shrink spell so that he could get under the door then dispels the effect from himself so he could revert to normal size. Quite the precarious position she was in and something he did not expect when she had tied herself up for the enjoyment of this act. Clearly she had needed some attention and he was all too willing to oblige her.