There are 2 main problems with voice recognition software. The first is that they have to spend a period of time 'learning'. The second is that you have to speak to your PC, which may not suit all office environments.
As long as it is a reasonably modern PC there should be no compatability issues. The fact that it is networked is immaterial.
My advice would be for your sister-in-law to have a chat with personnel. RSI is a health and safety issue, and provided that she can suggest a reasonable solution they should go along with it.
A quiet word with the system administrator may help too.