Wilma is going to be picky about what kind of app fred is...
If Fred is a console app, it should be fairly easy for wilma to use a pipe to capture the output from fred and display it in her own (console)window.. This is afterall a bit like how MSDev displays the output of the compiler/linker.
If Fred is a GUI program, then it's still somewhat possible, although it'll require LOTS of work, since you'll have to trap all window creation and window messages, and pass them along from wilma to fred. Only recommended for ultra advanced programmers though. I started something along the lines of this myself a looong time ago, but was only able to get partial support for it working.
Generally, you can safely safe that if fred doesn't provide for having itself run in a client window of another app (typically this would be done via OLE/Com/ActiveX), the effort for making it do that anyway, are probably not going to be worth it.