Why is she considered so smart?

she's a srude buisness woman, & a telapath, there for she could steal knowlige from anyones mind.

Her dialogue, characterization, attitude, and actions, and even intent by many writers, expose her as smart? She is comparatively quite witty, and sharp, as well compared to many of the other X-Men besides Beast and Jean, funnily enough, her words can have sting as well, which was the more general definition of the word smart originally.  
 
She is quite business smart as well, and people smart, and last but not least, your choice of words for the title of thread, Emma is actually a very sharp dresser, sharp being another original definition of smart.