Its not the inputs, I believe I know what your issue can be!
I believe this rig actually comes with stretchiness if I am not mistaking. I think you duplicated the mesh of her body in the position of when she was stretched out or in, therefore whenever you turn the blendshape 0 to 1 it does the deformation of the mouth PLUS the deformation of the arms since those vertices are trying to reach its default position.
A quick fix can be the following, pay close attention though since it can get confusing if you are just starting. Click the duplicated mesh of the character, the mesh in which you made the nose deformation. Now hold the right mouse button and drag to "Vertex", now select all of the vertices of the arms on both sides.
Once that is selected, on the right hand side where your channel box is located at you will see "CVs (click to show)", click on that, now click the first top left box, scroll down and hold down "SHIFT" and click the bottom right box. Type in the number "0" now and press "ENTER", this should bring all of those selected vertices back to their original default position!
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