Printing problem

I have a user on my network that has a local hp deskjet printer installed to
her LPT port that she prints to most of the time. She also has a network
printer in her printers folder that she prints large documents to, which is
an HP laserjet 4300tn. When she is in Outlook, she prints an email by
clicking the print button which goes to her default printer which is her
local printer. A while later she will notice that the same email printed on
the network printer. What causes this and is there a fix for it?