She keep having small problems like for instance printing with OS X 10.5.8 to a windows shared printer works very sporadic. Some times the printer spooler would come up other times you would have to printer a couple of times before the spooler would come up when priting from Word 2008.
Also working on a docx document that was created in windows the formatting is out and sometimes the screen would go blank when she is busy typing.
The key here is to focus on the bigger picture, not the singular experience in a multi-platform environment.
Most, if not all, of the issues will not be present if the whole network switches.
More on topic to the original question... how to change the users to Mac.
I don't hold any belief that a seminar or educational session on advantages will ever sway any users in any which direction.
Personally they might not like what they have at the moment. Employees dont curse Microsoft when the pc crashes. They curse technology. They dont curse Intel when the servers go down, they curse technology. The average user wont even be able to give a clear definition as to what constitutes blame for the DVD drive not working. Half would just say something in the lines of "Its the whole thing thats messed up".
A major problem for you right now, is that one test subject has already (very likely) poisoned EVERYONE against the change.
Best scenario i can imagine for you, would be to simply state to the employees that "this is happening. deal with it."
Send a company memo announcing that you "WILL officially be changing on xxxxx date" and thats final.
Between now and that date however, the company will have to fork the bill for some basic Mac usage training for everyone, possibly in business hours.
As sad as it all might seem... THIS difficulty of progression is what M$ banks on. "Its just too much trouble"... is that the main thought in your head already? Thats exactly where they want you to stay.