(Just realizing that you might be reluctant to say for fear of judgement).

It could be a whole bunch of things. It might be that you feel that she would be the person who would feel the most hurt / upset - which doesn't meant that you want to hurt / upset her, but rather, that your fantasy is more about the fact that she really cares about you such that it would hurt her.

A fantasy can be a fantasy without there being longings / cravings / action urges towards its realization. I don't think that one needs feel ashamed of ones fantasies... But exploring them can be useful, yeah.

Really... At the end of the day only you can figure out what it means to you...

But sometimes peoples questioning can help you figure it out!