I claim the ornamental design for a sheet straightener, as shown and described.
FIG. 1 is a perspective view of the top of a sheet straightener with a cinching loop substantially spanning the space between the two halves of the “X.”
FIG. 2 is a perspective view of the bottom of the sheet straightener.
FIG. 3 is a top plan view of the sheet straightener.
FIG. 4 is a bottom plan view of the sheet straightener.
FIG. 5 is a first side view of the sheet straightener, the second side being a mirror image thereof.
FIG. 6 is a first end view of the sheet straightener; and,
FIG. 7 is a second end view of the sheet straightener.
Components shown in broken line depictions are included for environmental purposes and form no part of the claimed design.
The straps are shown broken away to indicate no specific length.