Here was my reasoning behind it. Sakura has a higher psyche. He didn't hang up entirely or block entirely so she got some contact. Who he was seeing or what he was disguising she doesn't know. Merely sensing the thought to use the spell is all she did. I didn't want to do more than that, but I kind of like Sakura being a smiling and happy pain in the ass.

I was thinking more of Fiona having a partial contact with Corwin at one point. It was probably later in the books.