I've got a little issue with how acting feminine makes for a good submissive but that a digression for another post. It sounds like she's just testing you. If you let her get away with it, she will just continue questioning you and will never respect you as her Dominant.

You need to clearly communicate what you are seeking in a submissive generally and what you expect from her in particular. Let her know that things will happen on your timetable and at your whim and that her actions are not acceptable. Be specific about what you are talking about (for example, seeking clarification of a command is okay but questioning your orders is not). True disrespect of your authority should not be handled with a spanking (she might enjoy that) but by a withdrawal of your attention--put her in a corner with her nose against the wall and ignore her. It won't take too long for the message to sink in.

I must admit I do encourage minor, bratty behavior in my sub but, then again, we both like it when I take her to task. You need to find a level that works for you--a broken sub is no good to anyone and a little fighting spirit keeps things exciting.