It is possible to flip an image over the X or Y axis by setting ImageRectSize to a negative value and ImageRectOffset appropriately. However, when an image is flipped over the X axis with ScaleType.Fit, the image will no longer respect the bounding width (AbsoluteSize.X < AbsoluteSize.Y).
I’ve included a video to demonstrate:
Expected behavior
I expect the image to fit the frame visually, regardless of whether the sizes include negative values or not.