i don't get it why did bella cover her mouth (i tink she was shocked या s'thing) as she saw edward attac james (ballestudio)can u help me..??

oh no! she was juts smelling and realizing that she was covered in blood and that Edward like might go crazy and that it must be hard on him. That is why Edward is having his in pain face on and bella is like oh no face on
And I also agree that she was also scared

I think that that is the first time that Bella actually saw Edward look like a vampire. He wasn't be carefull like he usually is around her. I believe it was because she was worried/scared.

she knew she was covered in blood and was worried about edward's bloodlust.

Ummm well i think that it was a little bit of both she was shocked to see Edward attacking like that and also Bella faints at the sight of blood and she was covered in it and Edward was pained a little because she was covered in blood and James hurt her and he didn't like that!!!!