Assuming that either your wife or yourself, or both, are registered with Magix as the "owner" of this software, log into your Magix account, go to My products, find the entry for SF Pro 12 and under a "Show more details" link you will find all the activations currently associated with that software. Deactivate any that are no longer needed or used.
Then try again to activate the software on your wife's laptop.
If it still fails, or you cannot access your Magix account, you will need to email infoservice@magix.net and request their help.