If the iPad is "Associated" with your Apple ID then it can only be transfered to another one 90 days from the day it was first associated.
What does "Associated" mean?.. If you have set up "Automatic Downloads" or downloaded previous iTunes purchases through the iTunes app on the iPad it will automatically be associated. If however you've just synced the iPad using a computer with your iTunes account (and been playing the content ect) that simply means its "Authorised".
To check what devices are associated with your Apple ID, go to iTunes, from the menu bar go, store > view my account > Under where is says 'iTunes in the Cloud' click Manage Devices. Here you can check the date it may have been associated, and also choose to remove it. Warning: Simply removing it will not reset or erase the 90 day counter.
If you cannot see the iPad, or it was longer than 90 days from when it was associated just remove it from your device list. Then you can use this iPad with your wife's iCloud account.
Now, I assume your wife wishes to sync her iTunes purchases with this iPad? Or are you trying to use the her iCloud account while continuing to use your iTunes account for purchased content? Note: This will only work if you yourself have a separate account for iTunes and iCloud! Do you recall using your iTunes account to setup iCloud on any of your devices including your computer, or did you create a different Apple ID?
It is recommended that you use the same Apple ID for iTunes purchases and iCloud. So I would recommend backing up your iPad to your iTunes and then 'Erase all content and settings' so your essentially setting it up as a new device. Then when your wife first turns it on she can enter her iTunes account details when it asks you for an Apple ID to set up iCloud.
For more information see:
Setting up iCloud: http://www.apple.com/au/icloud/setup/
Apple IDs and iCloud: http://support.apple.com/kb/HT4895#
Associating a device or computer to Apple ID: http://support.apple.com/kb/HT4627
I hope that helps Ruskin :]