It's very easy to do that if you're familiar with the Windows file system.

The savegame files are located in the folder where you installed Fish Tycoon (the default is \Program Files\Fish Tycoon, if you purchased the game directly from LDW). There can be up to 5 savegame files (one for each player name), FishSaveGame1.pts through FishSaveGame5.pts. You can just move those files to your daughter's new computer. It might be a good idea to stop time on all of the games first, just in case there's a delay. You don't want anything bad to happen to her fishies!