Good question.
Microsoft Paint lacks the tools to do what you are trying to do. To rotate and have an image that you can bring back into Model Builder you need more capable software
I use two products that are free that have tools I think you need.
The 1st one is PDFCreator from pdfforge,
http://www.pdfforge.org/
PDFCreator lets you print to various file formats including jpg and bmp. Unlike using a screen capture utility the resultant file is high resolution.
The 2nd software is GIMP, GIMP is an image processing program that is created from the talents of many programmers and is available at
http://www.gimp.org/downloads/
This program has the rotate tool that you need as well as the ability to save your rotated item in gif file format.
Gif type files can be imported into Model Builder
When saving in gif format make sure you make your file with a transparent background. For help with GIMP do a search of the topic that interests you in You Tube.
By the way we are Working on a Rotate Tool for version 2 of Model Builder, the code for this tool is currently partially finished. Let me know if you would like to beta test this tool when it becomes available.
Dave