FWIW Monica and Dave, its not hard to straighten in DPP.
Select photo. At top of screen click on Tools> Start Trimming/Angle Adjustment tool. Check grid (on right side) makes it easier to get right. Hover mouse over black area outside the photo, hold left mouse button down, move mouse and straighten.(Is that called click and drag??)
Click OK to save. Go play in your preferred software with straightened photo!