I don't have time to look how it would look like with your version, but it will something look like this:

Maybe different version and publickeytoken, but it has the font family in the name and ends with the name of a font.
Just delete the line, our configuration is very tolerant as every single line in the config will be recreated when needed. (but with defaults).

I will try this with her, thanks. Will I know what the font line is, that link shows these two paths:

C:\Users%USERNAME%\AppData\Roaming\Greenshot\ in Windows Vista and newer version or
C:\Documents and Settings%USERNAME%\Application Data\Greenshot\ in Windows XP

There is also the possibility that the font, this Lucida for Attachmate is corrupt, unfortunately I'm not an expert in fonts...

It seems to be an issue with fonts, maybe she used that font for a while in Greenshot and uninstalled it, Greenshot might still want to use it, probably it was the last font used in Greenshot before removing it.

Check the greenshot.ini and remove the font line in there.
Here is described where then greenshot.ini can be found http://getgreenshot.org/faq/where-does-greenshot-store-its-configuration-settings/

And please stop greenshot before modifying...

I will check if this is reproducible so a fix can be made, to prevent it from happening in the future.