"Please Confirm payment" Button is not showing up for one of my clients on her pc or mac -

"Please Confirm payment" Button is not showing up for one of my clients on her pc or mac - but it shows up for me. She says that when she clicks on the "Please click here to confirm this appointment" button that the "wheel" just keeps spinning and the "Please confirm ... payment" button never pops up for her, Is this a known bug? Can you help me direct her in any way? Here's the button that doesn't come up for her ... http://www.myhypnotherapistonline.com/images/pay3.jpg