is there a reason why she or anyone wants to open browser forms from Datasheet view? what scenario leads to that requirement? It is not a good practice to do that, and I'm not so sure she ever was actually able to do that. It definitely opens the XML file if you click on the XML form title (that's expected behavior), and as you know, it behaves that way for _every_ user.
I tested it to make sure, and it does not ever open in the browser when I try from Datasheet view, and that's true for both the filename and InfoPath type icon. Are you absolutely certain she was able to do that previously?
SharePoint automatically opens forms in the browser if the user doesn't have InfoPath, but that's an integration function of Forms Services, and that function is not available in Datasheet view, it appears.