odnson:

Lady Sif is a one-woman army when it comes to hunting someone down. It’s rare that she needs help, but I think the reason she asks S.H.I.E.L.D. for help is because she respects Earth. She knows Thor does, too. She doesn’t want to wreak havoc across Earth and possibly hurt other people, so she wants to enlist their help and say, “This is your world. Let’s be collaborative in how we go about this.” (Alexander)