That's a problem with too many machines, all that software that you have to remove. Either choose one without, or remove it.
The right sequence:
1. Uninstall the trial.
2. Install the version she already has.
Kees
My sister is thinking about getting a new Toshiba laptop that comes with Microsoft Office Professional 2007 90 day Free Trial. She already has a CD of Microsoft Office Student and Teacher 2007 which she would like to use with the new computer. Will this present a problem or issues installing MS Office Student and Teacher 2007 over the MS Office Professional 2007 90 day Free Trail which comes with the new system?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic